Technical Course Manual Basic Level En

8/12/2019 Technical Course Manual Basic Level En

1/86

GENERAL CONTENTS CHAPTER

CHART

ANGELO PO GROUP

STAINLESS STEEL AND OTHER MATERIALS

GAS

ELECTRICITY

I/96


2/86

STAINLESS STEEL AND

OTHER MATERIALS

CONTENTS

CHAPTER 2

CHART?

STAINLESS STEEL:

GENERAL FEATURES

MAIN TYPES OF STAINLESS STEEL

AND THEIR TECHNOLOGICAL FEATURES

CLEANING STAINLESS STEEL

I/96


3/86

STAINLESS STEEL

AND OTHER MATERIALS

STAINLESS STEEL: G ENERAL FEATURES

CHAPTER 2

CHART 1

Stainless steel is an iron (Fe) alloy with a low carbon (C ) content, a high chromium (C r)content, mixed with other elements such as nickel (Ni), molybdenum (Mo), manganese

(Mn), silicium (S i), etc.

Only steel with a chromium content of not less than 11% may be defined as stainless.

Stainless means that the steel type is immune to the etching of the oxygen of air. Its

strength derives from a thin molecular coat of chromium oxide formed on the surface of

the metal, which protects it from further oxidation. There are a few substances, however,

which are capable of changing and destroy ing this coat and of starting corrosion

phenomena. These are chlorine and sulphur derivatives, which not only prevent the

reformation of the protective oxide coat but even corrode the stainless steel itself and

may create irrep arable damage. Maximum care to avoid this must therefore be taken,esp ecially by choosing the detergents to be utilized for cleaning with great care.

STEEL TYPES

STEELFe+C (2%)

STAINLESS STEELFe+Cr (11%)+C

ALLOYSTEEL

NON-ALLOYSTEEL

MARAGING STAINLESS STEEL

Fe+Cr (11+18%)++C (0.08+1.2%)

FERRITIC STAINLESS STEEL

Fe+Cr (13+30%)++C (0.08%)

AUSTENITIC STAINLESS STEEL

Fe+Cr (17+26%)++Ni (7+22%)+C (0.03+0.25%)

LOW ALLOYSTEEL

I/96


4/86

STAINLESS STEEL AND

OTHER MATERIALS

MA IN TYPES OF STAINLESS STEEL AND

THEIR TECHNOLOGICAL FEATURES

CHAPTER 2

CHART 2

AUSTENITIC STEELThe type of stainless steel of most widespread use on the market is austenitic steel, in particular

the type called AISI 304.

This is the basic type of austenitic stainless steel.

A series of steel types derive from this basic steel compound, capable of improving

some of its p roperties.

STEEL RESISTANT

TO CORROSION

AND HIGH TEMPERATURES

321 , 347

WELDING STEEL

304L 316L 317L

CUSTOMIZED

STEEL

STEEL RESISTANT

TO LOCALIZED

CORROSION

316 , 317

STEEL OF IMPROVED

MECHANICAL PROPERTIES

PRECIPITATION

HARDENING STEEL

304

(18% Cr - 10% Ni)

REFRACTORY STEEL

309 , 310 , 314 , 330

DUPLEX STEEL

RESISTANT TO

CHLORIDE CORROSION

ADDITION OF

Cr and Ni

ADDITION OF Cr

REDUCTION OF Ni

ADDITION OF

MoADDITION OF

Ni , Mo , Cu, Nb

ADDITION OF

Ti , Nb

ADDITION OF Mn and N

REDUCTION OF Ni

REDUCTION

OF C

ADDITION OF

Cu , Ti , Al

REDUCTION OF

Ni

MARAGING STAINLESS STEEL

The maragingstainless steel types are chosen for their mechanical prop erties, in p articular

for their hardness, but they should not be used in highly corrosive environments.

FERRITIC STEEL

Ferritic steel is easily worked by cold-processing and has a fine corrosion resistance

comp ared with maraging steel, although clearly less resistant than austenitic steel.

I/96


5/86

STAINLESS STEEL AND

OTHER MATERIALS

CLEANING S TAINLESS STEEL

CHAPTER 2

CHART 3

ROUTINE CLEANING

Steel surfaces must be thoroughly cleaned regularly using a damp cloth; soap and

water or ordinary detergents may be used, provided they do not contain

abrasives or chlorine-b ased substances such as sodium hypochlorite (b leach),

hydrochloric acid, or other solutions, since these products quickly cause irreversib le

corrosion of stainless steel.

Never use the substances listed above for cleaning floors under or near to

appliances since vapours or drops may have equally destructive effects on

the steel.

When detergents of any kind are used, surfaces must always be rinsed with water

and dried thoroughly.

I/96


6/86

STAINLESS STEEL AND

OTHER MATERIALS


CHAPTER 2

CHART 4

PRECAUTIONS REQUIRED

Sauces

All stainless steel containers used to contain ingredients known to be acid (vinegar, salt,

lemon juice, tomato p uree, etc.) must be washed thoroughly after use to remove all

residues.

Never allow salty solutions to evaporate, dry or remain for long p eriods on stainless

steel.

Salt

If salt deposits on the bottom of containers, it may trigger corrosion.

To avoid this, do not salt water until it has come to the boil.

Periods out of use

If equipment is to be unused for a long period (in case of seasonal use), clean the

outside stainless steel surfaces, and protect them with a film of vaseline oil or other

commercially availab le oily p roducts. As well as giving the steel a uniform appearance

and improv ing its gloss, this will prevent penetration by moisture and dirt, which also

causes of corrosion. These p roducts are now also availab le in spray cans, easy and

convenient to apply.

I/96


7/86

STAINLESS STEEL AND

OTHER MATERIALS

CLEANING S TAINLESS STEEL

CHAPTER 2

CHART 5

Traces of food

Wash with hot water before any food residues harden. If the residues are already hard,

use soap and water or chlorine free detergents, with the aid of a wooden spatula or fine

stainless steel scouring pad if necessary; rinse and dry thoroughly.

Never use blades or sharp scrapers which may scratch or damage surfaces.

Scratches

If the surfaces are accidentally scratched, smooth out the mark by rubbing with very fine

stainless steel wool, or abrasive sp onges made from fibrous synthetic material, in the

direction of the satin finish; rinse well and dry. Never use ordinary steel scouring pads for

cleaning stainless steel, since even small deposits of ferrous materials may trigger

oxidation.

Avoid any prolonged contact between ferrous materials and stainless steel.

Rust marks

The pipes of the water supply systems which supply pans, sinks, kitchens, etc.

inev itab ly shed ferrous material which dissolves in the water, particularly in recently

installed systems or after a period of inactivity. These ferrous deposits must not be

allowed to remain on the stainless steel, since they produce corrosion by contamination.

Make sure that systems are constructed using well galvanized pipes, and allow the

water to run for some time before starting to use it on each occasion. To remove any rust

marks which have formed, use suitable p roducts, contacting comp anies which p roduce

detergents for industrial use. After application, rinse with plenty of pure water and then

neutralize the effect with a detergent normally used for cleaning the equipment, or with a

specific product suitable for the p urpose.

N.B. Take care to avoid contact with parts not in stainless steel!

I/96


8/86

STAINLESS STEEL

AND OTHER MATERIALS


CHAPTER 2

CHART 6

TYPEOF DIRT RECOMMENDEDCYCLE COMMENTS

TRACES OF

ADHESIVES

(LABELS,

PROTECTIVE

COV ERINGS, ETC.)

REMOV E W ITH PETROLEUM SPIRIT, T URPENTINE OR OTHER

ORGANIC SOLVENTS

WASH WITH SPONGE,

WITH ORDINARY DETERGENTS OR SOAP

RINSE WITH PLENTY OF WATER

DRY WITH SOFT C LOTH

OR WIN DOW-LEATHER

Never use blades to scrape

away (use fine abrasives for

non gloss finishes, rubbing in

the direction of the satin

finish).

PLASTER, CEMENT,

SCALE

COMMERCIAL PHOSPHORIC ACID BASED SOLUTION OR

PASTE



OR WIN DOW-LEATHER

Soft nylon brush (on gloss

finish) "scotch brite" pad for

polished or satin finishes,

rubbing in the direction of the

satin finish.

OIL AND GREASE,FIN GER MARKS

PETROLEUM SPIRIT, SOLV ENT, ACETON E

WASH WITH SPONGE

(SOAP AND W ATER)



OR WIN DOW-LEATHER

LIGHT WATER

MARKS

WASH WITH SPONGE (NYLON BRUSH)

WITH SOAP OR ORDINARY DETERGENTS


DRY WITH CLOTH

Avoid contact with hands

(wear gloves).

SCALE

AQUEOUS SOLUTION W ITH VINEGAR

(25% vo l.)

RINSE W ITH PLENTY OF WATER AND BRUSH

DRY

Never use hydrochloric acid

Never use abrasives for 2B/BA

finishes.

I/96


9/86

GAS

CONTENTS

CHAPTER 3?

CHART ??

DEFINITIONS

CLASSIFICATION OF GASES AND FAMILIES

CLASSIFICATION OF APPLIANCES

PRESSURES OF GASES REACHING THE APPLIANCE

CALORIFIC VALUE OF THE REFERENCE GASES

CONVERSION FACTORS

COMBUSTION

KEY TO THE MOST COMMONLY USED EXPRESSIONS

BURNERS WITH PREMIXING

MULTI-GAS BURNERS

PILOTED FLAME BURNERS

SELF-STABILIZED FLAME BURNERS

SAFETY DEVICES

General

Safety devices

LIQUIFIED PETROLEUM GASES

General

Storage

Mobile containers (cylinders and drums) and fixed

containers

Cut-off, control and safety devices

Storage plant with movable containers

Plant dimensioning

I/96


10/86

GAS

DEFINITIONS

CHAPTER 3

CHART 1

TERM SYMBOL DEFINITIONG as (gaseous fuel) Any sub stance in aeriform state suitab le for use in

app liances for the p roduction heat, the comp letecomb ustion of which does not cause p rob lems withrelation to corrosion and health.

Volume of a gas in normalconditions or normal volume Vn

Volume measured in the dry state, at 0 C and at 1013mbar (760 mmHg).Exp ressed in m3n (normal cub ic metres).

Density of a gasin relation to air d

Ratio between the weight of a volume of gas and theweight of an equal volume of air, b oth in normalconditions.

Pressure of a gas Relative pressure, measured immediately up stream of

the user ap p liance in operation.Exp ressed in millibar (mbar).

Headloss Difference b etween the static p ressures measured intwo p oints of a system with one or more user ap p liancesin op eration. Exp ressed in millibar (mbar).

Calorific value of a gasH

Quantity of heat made availab le b y effect of thecomp lete combustion, at constant pressure, of 1 m3 ofdry gas, when the products of combustion have returnedto the initial temp erature.Exp ressed in kilocalories p er normal cubic metre(kcal/m3n) or in megajoules p er normal cubic metre(Mj/m3n).

Gross calorific valueof a gas Hs Calorific value of the gas, including the heat fromcondensation of the water vapour formed duringcomb ustion. For gases containing hydrogen.Exp ressed in kilocalories p er normal cubic metre(kcal/m3n) or in megajoules p er normal cubic metre(Mj/m3n).

Net calorific value of a gas

Hi

Calorific value of the gas, not including the heat fromcondensation of the water vapour formed duringcomb ustion. For gases containing hydrogen.Exp ressed in kilocalories p er normal cubic metre(kcal/m3n) or in megajoules p er normal cubic metre(Mj/m3n).

Gross Wob b e index Ws Ratio between the gross calorific value of the gas andthe square root of its density.

Net Wobb e index Wi Ratio b etween the net calorific value of the gas and thesquare root of its density.

Volume flow-rate qv Standard volume of gas consumed in the unit of time.Exp ressed in cubic metres p er hour (m3/h)

Weight f low-rate

qm

Weight of dry gas consumed in the unit of time at thetemperature of 15 C and at the p ressure of 1013 mb ar.Exp ressed in kilograms p er hour.

Thermal power absorptionQa

Quantity of heat corresp onding to the p roduct of thevolume or weight flow-rate for the resp ective calorificvalues of the gas referred to the same measuringconditions. Exp ressed in kilowatts (kW)

Rated thermal power QaN Thermal p ower ab sorp tion declared b y the manufacturer.

I/96


11/86

GAS

DEFINITIONS

CHAPTER 3

CHART 2

TERM SYMBOL DEFINITIONThermal p ower outp ut

Qr

Quantity of usab le heat sup p lied in the unit of time b y ab urner or b y a user ap p liance in sp ecific conditions.Exp ressed in kilowatts (kW).

Rated thermal poweroutput

QrN Thermal power outp ut declared b y the manufacturer.

Kilocalorie kcal Quantity of heat required to raise the temperature ofone Kg of distilled water from 14.5 to 15.5 C.

Efficiency

Ratio b etween the thermal power output and thermalp ower absorption, with the two quantities exp ressedwith the same unit of measurement.

Conventional room

temp erature

Reference temperature for trials, set at 20 C.

I/96


12/86

GAS

CLASSIFICATION O F GASES AND

CHAPTER 3

CHART 3

CLASSIFICATION (definition)Gases are classified in families on the basis of their characteristics; appliances are

classified in categories in accordance to the families of gases they are able to use.

CLASSIFICATION OF GASES

The gases which may be used are divided into three families, on the basis of their net

Wobbe index value (at 15 C and 1013 mbar).

FIRST FAMILY: manufactured gases

Wobbe index Wi: between 19.48 and 21.76 MJ/m3

Group abetween 19.48 and 24.40 MJ/m3Group b

between 22.10 and 22.14 MJ/m3Group c

between 16.70 and 21.27 MJ/m3Group d

between 19.03 and 20.65 MJ/m3Group e

SECOND FAMILY: natural gases

Wobbe index Wi: between 41.11 and 49.60 MJ/m3Group H

between 36.82 and 49.60 MJ/m3Group E(E+, Er)

between 40.52 and 49.60 MJ/m3Group E

(Es)

between 35.17 and 40.52 MJ/m3Group L

between 30.94 and 40.52 MJ/m3Group LL

between 36.82 and 40.52 MJ/m3Group E

(Ei)

THIRD FAMILY: liquified petroleum gases

Wobbe index Wi: between 68.14 and 80.58 MJ/m3Group 3B/P

(3B, 3+)

between 68.14 and 70.69 MJ/m3Group 3P

I/96


13/86

GAS

CLASSIFICATION OF APPLIANCES

CHAPTER 3

CHART 4

Appliances are classified as follows on the basis of the type and number of gases theyare able to use:

Category I

Contains appliances designed to use gases from one family only.

E.g.: category I 2H:

I indicates that the appliance belongs to just one family;2 indicates that the appliance belongs to the second family;

H indicates that the appliance belongs to group Hof the second family.

Category II

Contains appliances designed to use gases from two families.

E.g.: category II 1a2HL:

II indicates that the appliance belongs to two families;

1 indicates that the appliance b elongs to the first family;

a indicates that the appliance belongs to group ain the first family;

2 indicates that the appliance belongs to the second family;

H indicates that the appliance belongs to group Hof the second family;

L indicates that the appliance also belongs to group L

of the second family.

Category III

Contains appliances designed to use gases from three families.

E.g.: category III 1a2H3+:

III indicates that the appliance b elongs to three families;

1 indicates that the appliance b elongs to the first family;

a indicates that the appliance belongs to group ain the first family;

2 indicates that the appliance belongs to the second family;

H indicates that the appliance belongs to group Hof the second family;

I/96


14/86

GAS

PRESSURES OF GASES REA CHING THE APPLIANCE

CHAPTER 3

CHART 5

PRESSURES OF GASES REACHING THE APPLIANCE (in accordance with EN 203-1)

COUNTRY GAS TYPE

AND FAMILY

RATED

PRESSURE

MINIMUM

PRESSURE

MAXIMUM

PRESSURE

ITALY

GREECE

IT

GR

III FAMILY

G30/31

29/37 mbar 20/25 mbar 35/45 mbar

II FAMILY

G20

20 mbar

17 mbar 25 mbar

I FAMILY

G110

8 mbar 6 mbar 15 mbar

DENMARK DK III FAMILY

G30/31


II FAMILY

G20


I FAMILY

G110


FRANCE FR III FAMILY

G30/31

29/37 mbar 20/25 mbar 35/45 mbar

II FAMILY

G20/25

20/25 mbar 17/20 mbar 25/30 mbar

I FAMILY

G130


SPAIN ES III FAMILY

G30/31

29/37 mbar 20/25 mbar 35/45 mbar

II FAMILY

G20


I FAMILY

G110/130


I/96


15/86

GAS

PRESSURES OF GASES REA CHING THE APPLIA NCE

CHAPTER 3

CHART 6

PRESSURES OF GASES REACHING THE APPLIANCE (in accordance with EN 203-1))

COUNTRY GAS TYPE

AND FAMILY

RATED

PRESSURE

MINIMUM

PRESSURE

MAXIMUM

PRESSURE

BELGIUM BE III FAMILY

G30/31

29/37 mbar 20/25 mbar 35/45 mbar

II FAMILY

G20/25

20/25 mbar 17/20 mbar 25/30 mbar

GREAT BRITAINIRELAND

GBIE

III FAMILYG30/31

29/37 mbar 20/25 mbar 35/45 mbar

II FAMILY

G20/25


GERMANY DE III FAMILY

G30/31

50 mbar 42,5 mbar 57,5 mbar

II FAMILY

G20/25


I FAMILY

G110/120/140


AUSTRIA AT III FAMILY

G30/31

50 mbar 42,5 mbar 57,5 mbar

II FAMILY

G20/25


PORTUGAL PT III FAMILY

G30/31

50/67 mbar 42,5/50 mbar 57,5/80 mbar

II FAMILY

G20


I FAMILY

G110


I/96


16/86

GAS

PRESSURES OF GASES REA CHING THE APPLIANCE

CHAPTER 3

CHART 7

PRESSURES OF GASES REACHING THE APPLIANCE (in accordance with EN 203-1))

COUNTRY GAS TYPE

AND FAMILY

RATED

PRESSURE

MINIMUM

PRESSURE

MAXIMUM

PRESSURE

HOLLAND NL III FAMILY

G30/31


II FAMILY

G25


SWEDEN SE III FAMILYG30/31 29 mbar 20 mbar 35 mbar

II FAMILY

G20


I FAMILY

G110/120


FINLAND FI III FAMILY

G30/31


II FAMILY

G20


NORWAY NO III FAMILY

G30/31


TYPEAppliances are classified in the following types on the b asis of the way in which the

products of combustion are removed:

type A: appliances not designed for connection to a duct for removal of the products of

combustion;

type B: appliances designed for direct connection to a duct for removal of the

products of combustion, or assisted forced ex traction system (for

example a hood equipped with a mechanical ex tractor fan).

I/96


17/86

GAS

CA LORIFIC VALUE OF THE REFERENCE GASES

CHAPTER 3

CHART 8

TABLE OF THE CALORIFIC VALUES OF THE REFERENCE GASES IN USE FOR THE EC MARK (UNDER EN 203-

1/PrA1) FOR USE FOR CALCULATION OF THE HOURLY CONSUMPTION RATES OF GAS APPLIANCES

GAS TYPE

and GROUP

P.C.I.

(Hi)

P.C.S.

(Hs)

IIIa

G30(Group B)

45,65 Mj/kg12,69 kW/kg

49,47 Mj/kg13,75 kW/kg

FAM.G31

(Group P)46,34 Mj/kg12,88 kW/kg

50,37 Mj/kg14,00 kW/kg

IIa

G20(Group H ; E..s)

34,02 Mj/mc9,46 kW/mc

37,78 Mj/mc10,50 kW/mc

FAM.G25

(Group L ; LL ; E..i)29,25 Mj/mc8,13 kW/mc

32,49 Mj/mc9,03 kW/mc

Ia

G110(Group a)

13,95 Mj/mc3,88 kW/mc

15,87 Mj/mc4,41 kW/mc

FAM.G120

(Group b )15,68 Mj/mc4,36 kW/mc

17,77 Mj/mc4,94 kW/mc

G130(Group c)

23,66 Mj/mc6,58 kW/mc

25,72 Mj/mc7,15 kW/mc

G140(Group d)

13,38 Mj/mc3,72 kW/mc

15,18 Mj/mc4,22 kW/mc

G150(Group e)

18,03 Mj/mc5,01 kW/mc

20,02 Mj/mc5,57 kW/mc

N.B. THE REFERENCE CHARACTERISTICS ARE:

DRY GAS AT 15 C AND 1013 mbar

I/96


18/86

GAS

CONVERSION FACTORS

CHAPTER 3

CHART 9

CONVERSION FACTORS

1 atm = 10.000 mm w.c.

(water column)

= 760 mm

MERCURY COLUMN

1 bar = 10.333 mm w.c.(water column) = 760 mmMERCURY COLUMN

1 mm

MERCURY COLUMN

= 13,62 mm

WATER COLUMN

1 kg / m 2 = 1 mm

WATER COLUMN

1 kcal / h = 0,001163 kW 1,1628 W = 1 kcal / h

1 kcal = 0,004186 MJ

1 kWh = 860 kcal

1 kWh = 3,6 MJ

1 MJ = 239 kcal

1 MJ = 0,277 kWh

1 mbar = 10 mm c.d.a. = 0,001 atm

I/96


19/86

GAS

COMBUSTION

CHAPTER 3

CHART 10

GENERAL

Combustion is the chemical combination at a sufficiently high temperature of a fuel

with oxygen (the combustion medium), followed by the generation of heat.

The heat generated for each type of fuel: the quantity of heat p roduced by the

comp lete comb ustion of a normal cubic metre of it (i.e. a cubic metre measured at

the temperature of 0 C and at the p ressure of 760 mm of mercury) is defined as its

"calorific value".

Methane gas has a calorific value of about 9600 Kcal/m3.

In methane (C H4), the combustib le elements are carbon (C) and hydrogen (H2),

which react with the oxygen (O2) in the air to give carbon dioxide (C O2) and water

vapour (H2O), respectively, as products of combustion.

I/96


20/86

GAS

COMBUSTION

CHAPTER 3

CHART 11

THE FLAMEAn aerated flame, meaning a flame in which gas arrives for combustion already mixed

with air (defined as primary air), consists of three typical zones (Fig. 1):

OUTER ZONE

MIDDLE ZONE

INNER ZONE (CONE)

BURNER HEAD

Fig. 1 - Various combustion zones in an aerated flame.

- an inner zone (known as the cone) at low temperature and greenish-blue in colour,

where the air-gas mixture is heated to the ignition temperature (500C; 600C), and

combustion is triggered at its tip ;

- a middle zone, blue in colour, the site of a comb ustion process the completeness of

which depends directly on how close the amount of air conveyed to it is to the

theoretical volume. Carbon monoxide and a small percentage of hydrogen are still

generally found in this zone; it has the highest temp erature, which is 2050C for

methane.

- an almost purp le outer zone, where the gas, partially ox idized in the middle zone,

comes into contact with the surrounding air (known as secondary air) and comp letes itscombustion.

When the gas burns with insufficient primary air, the flame is longer and b righter; the

central cone is lengthened to an extent which depends on the intake pressure, and the

formation of yellow spots is also noticed (reducing flame).

When the gas burns with too much primary air, the flame is short and difficult to see, and

has a purp le, pointed cone (oxidizing flame).

I/96


21/86

GAS

COMBUSTION

CHAPTER 3

CHART 12

The speed at which the phenomenon of comb ustion is prop agated in a gas/air mixtureis known as the ignition speed. It is measured in cm/sec. and varies dep ending on the

typ e of gas.

The flame comes away from the burner when the speed at which the gas/air mixture

leaves the burner exceeds the ignition speed of the gas, as a result of excessive gas

pressure or excess primary air.

Flame retraction or under-ignition occurs when the reverse occurs; in other words, when

the speed at which the gas/air mixture leaves the b urner is lower than the ignition speed.

This is due to insufficient gas p ressure.

Naturally, during prop er, efficient combustion the flame must not come away from the

burner and flame retraction must not occur, since b oth are dangerous.

As we have seen above, a stable flame is obtained when the speed at which the

mixture leaves the burner is the same as the ignition speed. For good comb ustion, a

burner injector of the right size and the correct primary air setting are essential; the gas

intake pressure must also be correct.

Fig. 2 shows the various shapes of the flame in different operating conditions.

AIR AND GASIN CORRECT

PROPORTIONS

TOO MUCHGAS OR

TOO LITTLE AIR

TOO MUCHAIR OR

TOO LITTLE GAS

NORMAL

FLAME

LONG

FLAME

SHORT

FLAME

Fig. 2 - Flame shape in relation to primary air proportions.

I/96


22/86

GAS

KEY TO THE MOST COMMONLY

USED EXPRESSIONS

CHAPTER 3

CHART 13

Flue gases produced by a gasThe combination of the products of combustion of the gas and any excess air. They are

measured in normal cubic metres (m3n).

Carbon monoxide content of flue gases

The percentage of carbon monoxide (CO) by volume in the products of combustion of

the gas, considered in the dry state and free from air.

Good combustion limitThe limit beyond which comb ustion generates soot and the carbon monoxide content is

not accep table under the specific standards for each typ e of appliance.

Health rating of a room

The percentage concentration by volume of carbon monoxide (CO) in the room

considered.

Conventional room temperature

Reference temperature of the room where the tests are performed. Set at 20 C.

Flame retraction

The phenomenon in which the aerated flame moves b ack through the outlets of a burner

towards the injector.

Stable flame

A flame showing no signs of detaching from the burner or of retraction, or of being

extinguished in any way, in specific test conditions.

Pilot flame or pilot

Permanent flame placed close to a burner to assure that it ignites when gas is fed in.

User gas appliance

Complex equipped with one or more burners and the relative regulator devices.

I/96


23/86

GAS


USED EXPRESSIONS

CHAPTER 3

CHART 14

Connection equipment of a user gas appliance

All the devices (p ipes, unions, etc.) which convey the gas from the user appliance inlet

connection to the b urners.

Train of a user gas appliance

The complex of p ipes and junctions rigidly connected to the user appliance to distribute

the gas to the b urners.

Flue pipe connection

Connection on the appliance by which the appliance is connected to the flue for removal

of the p roducts of combustion.

Regulator device

Device which affects the value of a parameter involved in op eration of the appliance.

The regulation may be carried out by hand or automatically.

Valve

Regulator device with a movable shutter, which controls the conditions in which the

gaseous fuel flows to the burner.

Normal opening direction of a regulator device

Direction in which the movable part of the regulator dev ice must be moved to obtain a

supply of gas.

Flow regulator

An automatic dev ice intended to maintain the flow-rate of a fluid at a more or less constant

value.

Pressure regulator

An automatic device which reduces the pressure to a more or less constant level.

I/96


24/86

GAS


USED EXPRESSIONS

CHAPTER 3

CHART 15

Thermostat or thermoregulatorAn automatic device which acts on the flow of the heating medium to keep the

temp erature of the room controlled at a more or less constant level. The most common

types are the room temperature thermostat, water thermostat and air thermostat.

Pressure switch

An automatic device which regulates the p ressure of the steam in the appliance.

Flame failure device

Automatic regulator or cut-off dev ice intended to prevent the occurrence of dangerous

operating conditions.

Thermal flame failure device

A complex of mechanical parts intended to maintain the flow of gas to the b urner only

when the p ilot flame is lit.

The most common typ es are the bimetallic strip, thermoelectric couple, expansion,

photoelectric cell and conduction types.

Non thermal flame failure device

A complex of mechanical parts intended to maintain the flow of gas to the b urner only

when sp ecific conditions are met (such as a given pressure, etc.).

Gas burner

A mechanical complex intended to b urn the gas.

Primary air for combustion of a gas

Normal volume of air mixed with the gas in the burner before combustion.

Expressed in normal cubic metres (m3n).

Secondary air for combustion of a gas

Normal volume of air drawn in during combustion.

Expressed in normal cubic metres (m3n).

I/96


25/86

GAS


USED EXPRESSIONS

CHAPTER 3

CHART 16

Burner diffuser or mixerA specially shaped duct inside the burner in which the gas is mixed with the primary air.

Outlet section

Opening in the burner from which the comb ustion mixture flows for ignition.

Flame cap

The end p art of the b urner, which may be detachable, and forms the outlet section.

Injector

A device whose outlet size (which may be adjustable) sets the volumetric flow-rate of

the gas supplied by the b urner.

Flame

Special feature of the thermal-luminous phenomenon of combustion.

Flame characteristics

The height and colour of the flame.

Flame height

The mean distance b y which the various flames in the total flame project from the burner.

Total flame shape

The overall configuration which the flame assumes as a result of the geometrical layout of

the outlets.

Aerated flame

The flame of a gas which is mixed with air before comb ustion.

Non aerated flame

The flame of a gas which only comes into contact with air during combustion.

I/96


26/86

GAS


USED EXPRESSIONS

CHAPTER 3

CHART 17

Appearance of yellow tips in a flame

When abnormal yellow colour begins to appear at the tip of an aerated flame.

Detached flame

The phenomenon in which the flame moves away from the outlets of a burner towards

the outside.

Gust guardA device intended to p revent gusts of air from forcing the products of combustion b ack

into the appliance.

This device ensures that any air gusts will not have any effect on the quality of

combustion.

Draught

Suction force generated b y the flue gases in the upper part of the appliance and the

chimney.

The vacuum caused by the draft is expressed in millimetres of water column (mm H2O)

Draught cut-off

Device which connects the flue gas circuit to the atmosphere at a given point to make the

appliance indep endent from the draught in the flue.

The gust guard is generally incorporated in this mechanism.

I/96


27/86

GAS


CHAPTER 3

CHART 18

The atmospheric burner, or burner with air premixing, is the type most widely found in

domestic applications.

GAS

AIR

APPLIANCE

1 2

In normal conditions of use, an atmospheric burner creates a b lue flame consisting of an

inside cone, surrounded by an area of less luminous flame.

These b urners have considerable flex ibility, since they are able to op erate with various

types of gases and through fairly wide pressure ranges.

During the last few years, the flexibility of atmospheric burners has been increased as a

result of research carried out in order to adapt their op eration to the growing variety of

gases distributed. Over the last decade, the discovery of natural gas deposits, the

availability of liquified petroleum gases (deriving from the growing power and greater

number of oil refineries) have created a pressing need for the development and

construction of more flex ible b urners, with the aim of inventing a "universal" burner, easily

adapted to use both low yield gases (3,500 kcal/m3) and high yield gases such as

L.P.G. (30,000 kcal/m3), distributed at pressures which may vary from 40 to 500 mm

H2O.

I/96


28/86

GAS

BURNERS W ITH PREMIXING

CHAPTER 3

CHART 19

VENTURI PIPE

GAS

COMBUSTIONSURFACE

GAS JET

GASINLET

AIRADJUSTING

PLATE

Surface burner Venturi Suction or mixing pipe

ELEMENTS OF BURNERS WITH PREMIXING

This typ e of burner is made up of the following main elements:

a) The fixed or adjustable-head outlet injector defining and controlling the gas flow and

sometimes determinantly contributing to the combustion.

b) The mixing chamber or mixing head through which the gas passes after having been

let out of the injector.

c) The choke p ipe or mixing p ipe in which gas is mixed with the p rimary air that the gas

has dragged out by suction.

d) The burner head, where the gas and the primary air are conveyed after mixing,

beyond which, through the outlet section, the combustion process starts.

In atmosp heric burners the air conveyance by means of the gas is b rought about b y

suction with a Venturi pipe.

The Venturi pipe is made up of two convergent-divergent sections (the chamber and

the mixing p ipe) with a very restricted angle. The two sections are often connected by a

short cylindrical section, which makes up the throttle of the Venturi p ipe and which is

also called the Venturi neck.

I/96


29/86

GAS


CHAPTER 3

CHART 20

The diagram clearly shows how the p rimary air is conveyed: the pressure of this fluid,virtually the same as atmosp heric pressure at the burner inlet, reaches its lowest value in

the restriction of the Venturi pipe. In other words, it gradually decreases in the convergent

section of the Venturi pipe (maximum gas speed and thus minimum static pressure).

The suction force which draws in the primary air is p rov ided by this vacuum, which also

depends on the characteristics of the fuel gas.

After the neck of the Venturi pipe, the p ressure curve climbs again, and the speed of the

gas is transformed into p ressure, until it reaches the head of the burner at a value slightly

higher than atmospheric pressure.

C

B

B

B

B

A A A A

C C C

INJE

CTOR

MIXIN

G

CHAM

BER NECK

DIFFUSER HEAD FLAME

ATMOSPHERICPRESSURE

VACUUM ZONE

Pressure distribution in the Venturi pipe

Lig Ld

dmax

dg

di

di= injector diameter; dg= neck diameter; dmax= maximum diameter;

Lig= distance between injector and neck; Ld= diffusor length

Main dimensions of a bu rner

I/96


30/86


31/86

GAS

"MULTI-GAS" BURNERS

CHAPTER 3

CHART 22

During the last few years, the need has been felt to equip domestic user appliances

with burners capable of adapting easily to various typ es of gas at different pressures,

without requiring comp lex adjustment procedures, or even rep lacement of burner parts.

In order to extend the use of gas appliances, manufacturers have designed b urners

which are able to meet the various requirements with just replacement or adjustment of

the injector and adjustment of the primary air.

This has led to the development of multi-gas burners, designed to prov ide significant

flame stabilization.

The focus of the prob lem is the fact that while a town gas tends to trigger a retracted

flame, with a natural gas the flame tends to detach. The most unstable, delicate part of

the flame is that in contact with the metal part, where there is normally a quenching effect

which may lead to critical temp erature zones. With its upward movement, the secondary

air also disturbs the flame and tends to make it unstable.

Attention has therefore been concentrated on the outlet sections, with special study of

cooking appliance burners, the most widely used.

Two important developments have been achieved in this field: piloted flame burners

and self-stabilizing flame b urners.

I/96


32/86

GAS

PILOTED FLAME B URNERS

CHAPTER 3

CHART 23

Auxiliary or p ilot flames are p laced at the base of the main flame; this p rotects the flamefrom the turbulence of the secondary air, while at the same time it contributes heat to the

base of the flame.

Piloting may be horizontal or vertical to the main flame.

MAIN SECTION

AUXILIARY SECTION

MAIN FLAME

PILOT FLAME

MAIN FLAME

PERPENDICULAR PILOTING PARALLEL PILOTING

Piloting systems

It must be borne in mind that although it p rotects the main flame against the turbulent

effect of the secondary air, the p ilot flame must not offer too great an ob stacle to contact

and the p assage of the air.

Higher unitary thermal loads are possible with piloted flame burners than with

conventional b urners.

Ob viously, this means that smaller, higher power burners can be produced, extremelyuseful when space is limited.

I/96


33/86


34/86

GAS

SAFETY DEVICES

CHAPTER 3

CHART 25

GENERALCompared to other types of fuel, natural gas offers a series of advantages linked on the

one hand to the relative ease with which it can be ob tained, transported and used, and

on the other to the fact that its can easily be made safe and non-pollutant for the

environment.

Since the subject of this article is SAFETY DEVICES, we believe it is useful to start by

listing the potential risks related to the use of gas, and the possible effects of these risks.

We will then list the safety devices used to make the use of fuel gas safe, and explain

their op erating p rinciples and fields of application.

THE CONCEPT OF SAFETY

The concep t of safety is very wide and covers a great variety of aspects which can be

placed in order of decreasing importance on the b asis of the potential risks involved.

SAFETY: means preventing the escape of unburnt gas (danger of suffocation,

poisoning and explosion).

SAFETY: means preventing pollution of the room by the combustion products (danger

of suffocation and poisoning).

SAFETY: means preventing abnormal increases in temp erature (danger of scorching,

burns, explosions and fires).

This list of terms: "suffocation, poisoning, explosions, fires" immediately gives the

impression that we should keep as far away from gas as possible, since it is so

dangerous.This is not true: if prop erly used, gas is not only healthy, environment-friendly and

convenient, but above all safe.

Modern technology prov ides the appliance manufacturer - and thus the unit - with a

whole series of information, materials and devices (i.e. the safety devices) which make

the use of gas intrinsically and extrinsically free from all risks.

I/96


35/86

GAS

SAFETY DEVICES

CHAPTER 3

CHART 26

EFFECTS OF THE RISKS RELATED TO THE USE OF FUEL GASES

LEAKAGES OF UNBURNT GAS

This may cause two effects: suffocation and explosions.

We will be discussing a third possible effect, poisoning, in relation to the risks related to

the leakages of combustion products.

The virtually total disappearance of town gas has meant that this risk has almost been

eliminated in relation to gas leaks.

a) Suffocation:the gas replaces the air in the room, reducing its oxygen content, and thus

impedes the oxygenation of the blood.

b) Explosion:when the gas in the room has reached a concentration b etween the upper

and lower flammability limits, a spark generated b y any electrical appliance is enough

to trigger an explosion.

The lower flammability limit is approx imately:

Town gas 5-7%

Natural gas 4-5%

Liquified petroleum gas (LPG) 1-3%

With regard to the energy sufficient to trigger an explosion, purely as a guideline and to

give an idea of the orders of magnitude, the following are the values indicated by the

American Petroleum Institute.

Air-methane mixture 0.6-0.7 mj

Air-propane mixture 0.1-0.6 mj

Air-butane mixture 0.1-0.6 mj

For comparison, the energy needed to ignite a mixture of air and domestic heating oil

vapours is at least one order of magnitude greater.

I/96


36/86

GAS

SAFETY DEVICES

CHAPTER 3

CHART 27

NOTE

If we assume there is a gas leak flow-rate (expressed in cubic metres p er hour) of Ain a

room having volume V, in which the number of air exchanges per hour is G, the mean

percentage concentration of the gas in the environment varies exponentially over time t

in accordance with the formula:

Concentration (%) = 100 (A / (GV + A )) (1 - e EXP (Vt / (GV + A))

where "e" is the b ase of the natural logarithms.

The formula allows calculation of the mean concentration, or the concentration which there

would be if the gas were uniformly distributed throughout the room.

The formula clearly shows that there is no risk of explosion if the room in which the gas

leak may occur is large enough in relation to the possible leak flow-rate, and if adequate

air exchange is guaranteed.

In reality, and particularly with gases heavier than air (LPG), there may be zones with

different concentrations in the same room, and so in practice the lower flammability limit

may be reached locally, even if the theoretical conditions indicate a lower concentration:

- either because enough time has passed since the moment when the leak started;

- or because the volume of the room and the number of air exchanges are sufficient to

ensure that this critical percentage is never reached.

ABNORMAL TEMPERATURE INCREASESThese may occur either on the outside of an appliance (risk of the appliance itself or

surrounding items catching fire) or in the heated fluid (risk of explosion).

The consequences of an excessive temp erature increase may be particularly serious in

tanks (boilers or water heaters) which are not equipped with an open expansion tank.

I/96


37/86

GAS

SAFETY DEVICES

CHAPTER 3

CHART 28

SAFETY DEVICESThese are generally governed by clearly specified technical standards.

These standards are in force in virtually all countries, although there are differences

between one country and another. In Italy, they are drafted by the Cig and published

by the UNI, and they are generally approved in the form of a decree in accordance with

law 1083 dated 6 December 1971.

The CEN is working hard to make the safety standards identical for all memb er countries,

in order to allow free trade in appliances and dev ices.

CLASSIFICATION

Depending on their function, safety devices are subdivided into:

a) flame failure safety devices;

b) cut-off devices (solenoid valves etc.);

c) pressure regulators

d) thermostats and temperature limiters;

e) pressure switches;

f) devices for prevention of internal gas leakages;

g) atmosp here control devices.

FLAME FAILURE SAFETY DEVICES

They prevent the escape of unburnt gases. They may be of two types:

- single safety(if the flame fails, the passage of gas to the main burner only is cut off);

- complete safety(the supply of gas to the p ilot flame is also cut off).

Their main technical characteristics are:

- the ignition delay time(the time interval between the moment when the flame is lit and

the moment when the cut-off element automatically remains open);- safety time at flame failure(time interval between the moment when the controlled flame

goes out and the moment when the gas flow is cut off).

Finally, they may be divided into two categories:

- safety devices sensitive to the thermal prop erties of the flame;

- safety devices sensitive to the electrical and radiation prop erties of the flame.

I/96


38/86

GAS

SAFETY DEVICES

CHAPTER 3

CHART 29

SAFETY DEVICES SENSITIVE TO THE THERMAL PROPERTIES OF THE FLAMEThe most common, particularly in the lower power range (< 40 kW) are the

thermoelectric type.

Thermoelectric safety devices

They have the following advantages:

- they are self-supplying (they do not require an external power source);

- they provide total, positive safety conditions;

- they are easy to install and maintain.

The comp rise:- sensor element;

- magnetic safety unit;

- valve body.

They are generally accompanied b y the following accessories:

- p ilot b urner;

- igniter;

- ignition cut-out;

- interlock.

a) Sensor element

This makes use of the thermoelectric prop erties of metals. Let us consider two metal

wires in different materials (e.g. nickel-chrome and constantan) welded together at one

end (hot junction C) and closed at the other end (known as the cold junction D) on an

ohmic load R(fig. 1).

CD

R

mV

Fig. 1

I/96


39/86

GAS

SAFETY DEVICES

CHAPTER 3

CHART 30

If the hot junction C is exposed to a heat source, the phenomena described belowoccur.

A difference in electrical potential (voltage) is established b etween the two junctions (hot

junction Cand cold junction D) at different temperatures, and this causes a current to

circulate in the circuit. This p otential difference (voltage) is p rop ortional to the difference in

temperature between the two junctions.

This principle is widely used for measuring temperatures.

However, when a temperature is measured using thermocouples the first essential

condition is that the cold junction must be at constant temp erature, meaning that it is not

subject to variations while the measurement is being made. It is therefore p laced as far

as possib le from the heat source.Conversely, in a safety thermocouple the cold junction Dis at a very small distance (20-

30 mm) from the hot junction C, and is connected in turn to the load R by means of a

suitab le conductor (fig. 2).

C

D

R

mV

Fig. 2

During operation, this cold junction Dis also heated, and the temperature generates a

voltage contrary to that generated at the hot junction C, meaning that the voltage

available across Ris reduced.

Safety thermocouples are designed in this special way in order to reduce the voltage

more quickly during cooling: when the flame fails, the temperatures at Cand Dtend to fall

to the same level quickly, and thus the supply of power ends more quickly.

I/96


40/86

GAS

SAFETY DEVICES

CHAPTER 3

CHART 31

In practice, from an electrical point of v iew, the thermocouple can be shown in diagram

for as in fig. 3, where:

E1 E2

R

Fig. 3

E1= 0.07 T1 mV (T1 = temperature of hot junction C)

E2= 0.05 T2 mV (T2 = temperature of hot junction D)

R= ohmic resistance of the conductors.

In typ ical op erating conditions, the thermoelectric force generated b y a thermocouple is

of the order of 20 mV. Since its ohmic resistance is of the order of 20 milliohms, the

maximum usable power which can be ob tained from a generator of this kind is of the

order of a few milliwatts.Another important feature of the safety thermocouple is that it is constructed with a

coaxial shape, in order to make it stronger and easier to handle, while the material with

the best resistance to the effects of the flame (temp erature, corrosion, etc.) is on the

outside.

I/96


41/86

GAS

SAFETY DEVICES

CHAPTER 3

CHART 32

Figure 4 gives the actual shape of a safety thermocouple, while figure 5 shows the trendof the thermoelectric force available across it at ignition and switch-off.

C

1

1

2

3

4

CD

2

D

4

3

Electronegative element

Electropositive element

Copper conductor

Copper conductor

Hot junction

Cold junction, or oppositionjunction

TIME (seconds)

VOLTAGE(millivolts)

V1

V2

T1

T0

mV

s

A

B

C

A - As soon as the flame ignites, the voltage quickly rises to the value V1.B - After some time, the voltage tends to fall (the cold junction also heats up)

and the voltage assumes a stable value V2.

C - When the flame goes out (moment T1) the voltage falls until it disappears

altogether.

Fig. 4 Fig. 5

N.B.

The special shape of safety thermocouples means that they must be exposed to the

flame in such a way that it only touches the hot junction C, meaning the tip. The lower part

(more than 8 mm from the tip) must never be touched by the flame or heated

excessively.

8 mm (max)

YES NOT!

Fig. 6

I/96


42/86


43/86

GAS

SAFETY DEVICES

CHAPTER 3

CHART 34

d) Pilot burnerThe p ilot burner is a small burner of low thermal power (normally below 200 W)

installed in a fixed position in relation to the main burner of the appliance, in order to:

- supply a permanent flame (p ilot flame) in order to assure ignition of the main burner

when gas is supplied;

- keep the end of the thermocouple heated during op eration of the appliance (safety

flame).

It may be of two typ es:

aerated(Bunsen type burner: the jet of gas from the nozzle passes through a Venturi

p ipe and carries draws in the p rimary air necessary for combustion) (fig. 9a):not aerated(so-called Target burner, in which the air necessary for combustion is drawn in

at the base of the flame) (fig. 9b).

Finally, it may have:

fixed injector(the injector outlet section consists of a hole of fixed size);

adjustable injector(the outlet section may b e varied using an adjuster screw).

Fig. 9a - Bunsen type aerated burners

Fig. 9b - Non aerated (Target) burners

I/96


44/86

GAS

SAFETY DEVICES

CHAPTER 3

CHART 35

e) IgnitersHere we are only discussing self-supplying (p iezoelectric) igniters.

Igniters which use outside electrical power will be considered when we discuss safety

devices sensitivity to the electrical and radiation prop erties of the flame.

Piezoelectric igniters make use of the electrical power generated in some materials (such

as barium titanate crystals) when they are subjected to a mechanical stress.

Figure 11 shows the trend of the open circuit electromotive force generated across a

cylinder of 20 mm of p iezoelectric material in relation to the p ressure applied to its two

faces.

00

5

10

15

20

25

10 20 30 40 50

COMPRESSIVE STRESS

OPEN

CIRCUITVOLTAGE

(kV)

20mm

+

-OPEN

CIRCUITVOLTAGE

Fig. 11

The usable energy which can be obtained from a piezoelectric ignition device is of the

order of a few mj, and the voltage of the order of the tenth of a kV.

Piezoelectric igniters are generally of two types.

Squeeze action igniter.

A compressive stress is applied to the crystal by means of a lever.

The main feature of this type of igniter is the relatively long time for which the loadapplied lasts; it continues for a few seconds and dep ends on the way in which the lever

is operated. During this time the generator charges and discharges several times,

causing a train of sparks which increase the p ossib ility of ignition.

This positive feature is counter-balanced by:

- very bulky size;

- the dev ice only works prop erly if perfectly dry. In view of the relatively long charging

period and the high voltages involved, even small amounts of ambient humidity may

prevent achievement of the discharge voltage.

I/96


45/86

GAS

SAFETY DEVICES

CHAPTER 3

CHART 36

Figure 12 illustrates a typ ical squeeze igniter.

PROTECTEDPIEZOELECTRICCRYSTAL HIGH VOLTAGE

TERMINAL TOWARDSTHE ELECTRODE

BURNEREARTHCONNECTION

SPIRAL SPRING

FIXED BRACKET

MANUAL OR CAM CONTROL LEVER

Impact igniter

A dynamic stress is applied to the crystal by means of a hammer loaded by a spring

(figure 13).

0

2

4

6

8

10

12

14

20 40 60 80 100 120 1 40

KW

s

The mechanical stress applied (and thus the voltage generated) depends on the impact

speed and the weight of the hammer. In general, these devices generate just one

voltage pulse lasting about 20 microseconds. This very short discharge time makes the

system less vulnerable to the effects of the leakage current (a resistance of 1 megohm is

more than sufficient).

A A B

C

D

IMPACT TYPE PIEZO ELECTRIC IGNITER

A CRYSTALS

B HAMMER

C MAGNET

D HAMMER SPRING

In view of the short stress time, the specific load may be increased with no risk of

damaging the crystal (greater energy availab le in smaller sp ace). The system is small in

size and easily integrated into a compact multifunction unit.

I/96


46/86

GAS

SAFETY DEVICES

CHAPTER 3

CHART 37

f) Ignition cut-outThis dev ice p revents the igniter from op erating as long as the main gas circuit is open.

Basically, it consists of an electric contact operated by the button which also resets it, in

series with the ignition electric power supply circuit.

Figure 15 shows the ignition cut-out of the Babysit valve in diagram form.

Fig. 15

g) Interlock

This prevents the spool from reopening throughout the safety time at turn-off.

It can be only be fitted on valves with hand-operated shut-off tap.

When the user puts the appliance out of op eration by turning off this tap, a mechanical

lock-out device is engaged to prevent the gas supply from begin turned back on aslong as the thermoelectric safety device is in open position.

The interlock generally acts on the main burner. However, in some cases it also acts on

the p ilot burner (comp lete lock-out). Figure 16 shows the interlock of the Comp osit

valve in diagram form.

C

A

E N F O P M S R L D

V

T

BEVTA

Fig. 16

When the knob Mis turned to Off, the spools Oand Dcut of the passage of the gases. The lever F, working with the cam R, locks the

knob and prevents the appliance from being put back into operation. It is not until the magnetic safety unit is tripped into closed position

that the lever Fis released, allowing the device to be operated again.

I/96


47/86

GAS

SAFETY DEVICES

CHAPTER 3

CHART 38

DESCRIPTION OF OPERATION OF A THERMOELECTRIC SAFETY DEVICEOperation is explained with the aid of figure 17.

The instrument shown in diagram form in the diagram is intended to illustrate the trend of

the electromotive force generated by the thermocouple during the various operating

phases.

Setting (fig. 17a)

When the setting button is pressed, the passage of gas to the p ilot burner is opened,

while at the same time the p assage of gas to the main burner is cut off.

Ignition is prov ided b y the p iezoelectric igniter, which triggers a spark between theelectrode and the ground.

After a few seconds (ignition delay time), the electromotive force generated by the

thermocouple is high enough to keep the magnetic safety unit attracted.

Fig. 17a

Normal operation (fig. 17b)

When the set button is released, gas also flows to the main burner.

I/96


48/86

GAS

SAFETY DEVICES

CHAPTER 3

CHART 39

Safety cut-out (fig. 17c)If the flame fails, the thermocouple cools.

When the electromotive force is no longer sufficient to keep the magnetic safety unit

attracted (i.e. when the switch-off safety time has passed) the spool, driven by the

spring, switches to closed p osition, cutting off the p assage of gas both to the main

burner and to the pilot burner.

Manual intervention is required to p ut the dev ice b ack into operation.

Fig. 17c

PRESSURE REGULATORS

These are installed to keep the burner supply pressure constant even in case of

variations of the pressure upstream.

Under CEN EN 88 they are divided into 3 classes on the basis of the type of flow-rate

(for fixed or variable flow-rate) and the permitted tolerance field.

a) Simple pressure regulator

The basic principle behind its operation is illustrated in figure. 18.

INLET OUTLET

VALVE

SEATING

VALVE

VALVE STEM

FLEXIBLEDIAPHRAGMWEIGHT

BREATHER HOLEV

Pi

P

Pu

MF

Fig. 18

I/96


49/86

GAS


CHAPTER 3

CHART 40

GENERAL

The hydrocarbons prop ane and butane are known as "liquid gases" because they are

used in the gaseous state but stored and transported in the liquid state. The

comb inations of the constituent elements of these hydrocarbons are defined by the

formulae C 3H8and C 4H10respectively; they are usually indicated more briefly as C3and

C 4.

The term "liquid gas" does not claim to be correct: it is more accurate to describe them as

"liquified petroleum gases", or "L.P.G." for short. As already mentioned, prop ane and

butane are stored and transported in the liquid state, under pressure, in metal containers,

and evaporate as soon as the p ressure inside the container decreases.

The passage of a liquid to the gaseous state can be explained most simply by taking

water as an example.

Water is known as a slowly evaporating liquid; this slow evaporation is made possible

by the fact that at atmospheric pressure and at ambient temperature a certain amount of

water passes to the vapour state.

This passage becomes more accentuated as the temperature rises, and the vapour

applies a certain pressure known as the "vapour pressure" to the water. At the

temperature of 100C, this vapour pressure reaches the atmospheric pressure, and so

evaporation becomes much more turbulent and is known as "boiling". Thus at a

temperature of 100C all water passes to the gaseous state.

If the water is b oiled at a pressure above atmosp heric pressure, a higher temperature is

required before its vapour pressure reaches the ambient pressure; in this case, the

boiling point is higher than 100C .

I/96


50/86

GAS


CHAPTER 3

CHART 41

For example, at a pressure of 10 atmospheres, the boiling point of water is 180C. This

means that at a pressure of 10 atmospheres water continues to remain in the liquid state

at a temp erature over 100C, but at 180C it will start to boil. In other words, until 180C

its vapour pressure is lower than the overlying p ressure of 10 atmosp heres.

Conversely, if the surface of the water is exposed to a vacuum, the boiling point is

reached at a lower temperature, and the b oiling temp erature is b elow 100C .

The influence of temp erature and p ressure on the evaporation of water is thus obvious.

For propane the boiling temperature(which for water at atmospheric pressure is 100C and

represents the borderline between the liquid and gaseous states) is -43C, while for

butane it is 0C, both at atmospheric pressure. At a temperature below -43C at

atmosp heric pressure, p rop ane is liquid, while at higher temperatures it is gaseous. As

we have explained for the example of water, propane can be kept at the liquid state at

a temperature over -43C, prov ided a pressure greater than atmospheric pressure is

app lied to it.

For example, at the pressure of 5.5 atm, propane may be kept liquid at the temperature

of 10C. IN a cylinder containing propane at ambient temperature (e.g. 10C), we will

find just this phenomenon: the prop ane is in the liquid state, while above it there is a

"cushion" of vapour at the p ressure of 5.5 atm.

When the tap of the cylinder is opened, the liquid gas it contains escapes in gaseous

phase; after this discharge the pressure inside the container is slightly reduced, and as a

consequence of this reduction in pressure the liquid inside the cylinder comes back to the

boil, supp lying more gas by evaporation until the supply is cut off by closing the tap.

At atmosp heric pressure, the boiling point of the prop ane-b utane mixture is more or

less proportional to the mixture ratio; it is therefore between -43C and 0C.

I/96


51/86

GAS


CHAPTER 3

CHART 42

WHAT IS PRESSURE?It is the force which acts on the unit of surface area. We are surrounded by a pressure

determined by the weight of the air around us: this p ressure is called "atmospheric

pressure".

Pressure is measured in:

Atm. (atmospheres)

Kg/cm2

(kilograms per square centimetre)mmHg (mm of mercury column)

mm H2O

(millimetres of water column)

mm c.a.

In practice, Atm. (atmosp heres) and Kg/cm2 (kilograms per square centimetre) are

equivalent, meaning 1 atm = 1 Kg/cm2.

The small pressures of L.P.G.s at the user appliances are generally measured in mm of

water column. Since 1000 mm H2O are equivalent to 0.1 Kg/cm2, 1 Kg/ cm2 is

equivalent 10,000 mm of water column, or in other words a column of water 10 metres

high.

The concep t of the pressure applied by a gas enclosed in a container is as follows. A

body in the gaseous state takes the shape of the recipient in which it is contained and

tends to occupy the entire volume of the recipient. A body in the liquid state also

assumes the shape of its recipient, but if the quantity of liquid is less than the volume of

the container, the liquid only occupies the p ortion of the container which corresp onds to

its own volume. A body in the gaseous state therefore has free molecules mov ing in all

directions; the impacts of these molecules against the walls of the container determine

the p ressure of the gas in the container.

If the temp erature of the gas inside the container increases, the speed of the molecules

also increases, and the number of impacts against the walls rises too, giving an increase

in the pressure of the gas inside the container.

Therefore: the pressure which a gas applies inside a container is proportional to its temperature.

I/96


52/86

GAS


CHAPTER 3

CHART 43

The dimensions of recipients containing gases must b e calculated so that they will

withstand the normal op erating pressures of the gases they are to contain: for prop ane,

this pressure is 18 atm.

For a better understanding of the questions discussed in this section, we first need to

define the "calory" and explain the concep t behind it.

CALORY

When a combustib le substance burns, it generates heat which is measured using

special devices known as calorimeters.

The quantity of heat is measured using a unit known as the "calory", or:

1 the calory (cal), which is the quantity of heat needed to raise the temperature of 1

gram of water by 1C;

2 the kilocalory (Kcal), which is the quantity of heat needed to raise the temperature of 1

Kg of water by 1C.

Remember that to evaporate a liquid it must always be heated; in other words, a certain

amount of heat must be transferred to it. For example, for water at 0C , it will take

exactly 639 calories for one Kg (Kcal/Kg). It takes 100 Kcal ( Kg to reach the boiling

point of 100C starting from 0C. In addition, at the constant temperature of 100C a

further 539 Kcal/Kg is required to convert all the water from the liquid to the gaseous

state, and this evaporation heat, of 539 Kcal/Kg, must be provided by supplying

additional heat.

In the case of liquid gas, the cylinder is usually heated by means of the surrounding air,

but if this is not sufficient to allow total evaporation, the further heat required must be

ob tained from the contents of the cylinder. In other words, heat is taken from the liquid

contents of the recipient, which therefore cool. If large quantities are taken off, the

temperature of the liquid may drop below its boiling point (boiling temperature of

butane = 0C, propane = -43C), to the point where evaporation is interrupted.

I/96


53/86

GAS


CHAPTER 3

CHART 44

The degree of cooling of a liquid, or in other words of the removal of heat from it, thus

depends on the delivery speed /Kg/H). Since there may be evaporation problems

due to the consequences of the cooling produced by the removal of heat from the

liquid, this must be borne in mind when systems are designed, particularly if the p rocess

may also be affected b y low outside temperatures.

The maximum speed for supply of the gas inside a cylinder depends on the

composition of the gas, the outside temperature and the surface area of metal p late in

contact with the liquid.W ith continuous supply (i.e. when supply at the same rate continues for some hours),

and with an outside temp erature of 0C, as the commercial prop ane inside a container

begins to run out, it is possib le to ob tain a flow-rate of about:

- 0.300 Kg per hour from a cylinder of 20 Kg.

- 1 Kg per hour from a drum of 100 Kg.

With a temperature of 0C but with on/off delivery, the quantities of gas which can be

supplied per hour are about twice those indicated above.

The quantity of heat required to transform liquids at boiling point into gases, or the

evaporation heat, is:

- 102 Kcal for 1 Kg of prop ane

- 92 Kcal for 1 Kg of butane.

If all the evaporation heat is obtained from the liquid, the resulting drop in its temperature

can be calculated if its specific heat is known.

From experience, we know that if a given amount of heat is applied to identical

quantities (weights) of different substances, the temperature of each will increase by a

different number of degrees. This indicates a difference in heat absorption capacity,

which varies dep ending on the nature and p hysical state of the substances concerned.

I/96


54/86

GAS


CHAPTER 3

CHART 45

For example, special devices known as calorimeters can be used in experiments to

demonstrate that for every kilocalory applied to 1 Kg of lead, to 1 Kg of glass, and to 1

Kg of water, the temperature of the lead rises by 32C, of the glass by 5C and of the

water, as we have already seen, by 1C.

This fact demonstrates that every substance has its own heat capacity, which depends

on its nature and physical state.

The specific heat of a substance is the quantity of heat, expressed in kilocalories (Kcal) needed toraise the temperature of 1 Kg of it by 1 degree centigrade.

On average, for prop ane and butane in the liquid state, it is 0.55 Kcal.

For example, when 1 Kg of propane is supplied from a cylinder containing 20 Kg of it,

102 Kcal is taken from the other 19 Kg, and this is the evaporation heat of the prop ane

as defined above.

Bearing in mind that when 0.55 Kcal is removed from it, 1 Kg of liquid propane cools b y

1C, it would require absorption of 10.45 Kcal (0.55 x 19) to cool the 19 Kg left in the

cylinder by 1C.

In other words, for every 10.45 Kcal removed, the temperature of the 19 Kg of

prop ane left in the cylinder will fall by 1C .

Since we have removed 102 Kcal to evaporate the kilogram of propane (one of the 20

Kg inside the cylinder), the temp erature of the remaining liquid will have dropped by

102/10.45 = 9.7C.

This calculation will be correct if the liquid is unable to ob tain heat from the outsideenvironment during evaporation; if this is possible, naturally the cooling of the liquid will

be proportionally reduced.

The longer the liquid remains available (i.e. the slower the delivery flow-rate) the greater

the possibility that the liquid will be heated from the outside. This means that if a number

of gas cylinders are used in combination, the heat removal effect can be sp read over a

larger quantity of liquid.

I/96


55/86

GAS


CHAPTER 3

CHART 46

This short explanation shows how wrong it is to try to insulate a gas cylinder if the typical

symptoms of cooling (the formation of frost and even ice) are noticed on its surface

when gas is taken from it, since this would eliminate its only chance of absorbing heat

from the outside.

Another way of increasing the possible delivery rate is to use a vaporizer. Naturally, in

this case the L.P.G. must be taken from the tank or cylinders as a liquid, which is then fed

into the vaporizer heated by gas or electricity.

The evaporation yield of an electrically heated vaporizer depends on the absorption

capacity of the heating system. Taking an average evaporation heat of 102 Kcal/Kg and

bearing in mind that 1 KW h is equivalent to 860 Kcal, an amount of electricity of 102/860

= 0.12 KWh will be required for every Kg of L.P.G. to b e evaporated in an hour.

An electrically op erated liquid gas vaporizer, required to evaporate a total 5 Kg per hour,

will have to have a power of at least 0.12 x 5 = 0.60 KW = 600 Watts.

A gas heated vaporizer offers the advantage of independence from the electrical mains:

its efficiency can be assessed as around 80%.

As for the calculation given above (bearing in mind that 1 Kg of prop ane supplies

12,000 Kcal), the liquid gas consumption per Kg/h of evaporation output in continuous

service is 102 / (12,000 x 0.8) = 0.010 Kg/h = 10 grams/h.

Heating the contents of the cylinder or drum directly in case of evaporation prob lems is

dangerous, since the container may expand until it explodes.

At the most, the cylinder may be p ut inside a container of water heated to not more than

40C.

I/96


56/86

GAS


CHAPTER 3

CHART 47

STORAGE

HOW TO CALCULATE THE STORAGE CAPACITY REQUIRED

In a company using L.P.G. for industrial purposes, the storage capacity is generally

defined as the total capacity of the containers installed on its p remises to receive the

L.P.G. necessary for its requirements. This capacity is generally expressed by volume

(m3) or by weight (Kg).

When calculating the storage capacity a company needs, two apparently conflicting

requirements must be satisfied:

- on the one hand, the storage capacity must be limited in order to minimize theinstallation expenses and comply with the Fire B rigade regulations with regard to

safety distances;

- on the other hand, the company must be assured a stock of L.P.G. adequate for its

continuous operation (also allowing for the possibility of future increases in output, if

considered approp riate) without having to request deliveries from suppliers too often.

The stock of L.P.G. which a factory needs is generally determined by calculating the total

mean consumption of the all the company's user appliances and envisaging that

deliveries will normally be made at frequencies between 8 and 16 days.

FACTORS TO BE BORNE IN MIND WHEN CHOOSING CONTAINERS

The containers in use for storing L.P.G. on the consumer's p remises are of various

types and capacities, dividing above all into portable (cylinders and drums) and tanks.

For daily consumption levels up to 50 Kg of L.P.G., cylinders of 25 Kg are used, in

sufficient number to cover the p eriod between successive deliveries.

For daily consumptions between 50 and 150 Kg, drums of 100 Kg are generally used,

again in sufficient number to cover the period between successive deliveries.

For higher consumption levels, the L.P.G. is p laced in metal tanks having capacity of at

least 10 m3in order to benefit from the tax concessions currently available (at least inItaly).

Here again, the tanks are designed to allow a storage capacity which will assure the

op timum delivery frequency. It is only for plants at long distances from the L.P.G.

production centres that it is economically advantageous to use tanks of higher capacity

than necessary, to take full tanker loads and thus limit transport costs.

I/96


57/86

GAS


CHAPTER 3

CHART 48

MOBILE CONTAINERS (CYLINDERS AND DRUMS) AND FIXED CONTAINERS

CYLINDERS

The cylinders generally used for Pibigas industrial sales contain a net weight of 25 Kg of

L.P.G. Their construction data and gaseous p hase delivery capacities are:

- height 800 mm;

- diameter 320 mm;

- testing pressure: 35 Kg/cm2;

- explosion pressure: not less than 81 Kg/cm2

- tare weight: about 22 Kg (the tare weight is punched on the cylinder);

- continuous propane gas delivery at 0C: about 300 g/hour.

DRUMS

Net contents, 100 Kg of L.P.G.

They are fitted with two valves:

- one for delivery of vapour phase, and thus in direct communication with the top of the

drum;

- the other for delivery of the liquid phase, and thus connected b y means of a down line

to the bottom of the container.

Their specifications are:- height: 1500 mm;

- diameter: 500 mm (excluding rolling rims)

- testing pressure: 35 Kg/cm2;

- explosion pressure: not less than 81 Kg/cm2

- tare weight: about 100 Kg (the tare weight is p unched on the drum);

- continuous propane gas delivery at 0C: about 1 Kg/hour.

I/96


58/86

GAS


CHAPTER 3

CHART 49

METAL TANKSThese are cylindrical, with round or elliptical ends, constructed in steel p late of

appropriate type and thickness. They are approved for the operating pressure of 18

Kg/cm2, and tested at the pressure of 23 Kg/cm2. Supported by two reinforced concrete

saddles, they are placed horizontally, above ground or underground. They are most

often installed above the ground, but underground installation requires shorter safety

distances, although there are problems during annual inspections. Tanks installed

underground must be completely covered with sand by law, but for inspection all the

steel p late must be in view, and this means that all the sand has to be taken out of the

pit. Underground installation should thus be used only when there is no alternative. The

dimensions of the types of tank normally used are:

- tank of 20 mc - tank of 25 mc

length: 7.20 m length: 8.91 m

diameter: 2.00 m diameter: 2.00 m

weight: 67 q.li approx . weight: 80 q.li approx .

- tank of 50 mc - tank of 100 mc

length: 10.25 m length: 20.35 m

diameter: 2.65 m diameter: 2.65 mweight: 110 q.li approx. weight: 240 q.li approx.

Fig. 3 - Tank of 20 m3

I/96


59/86

GAS


CHAPTER 3

CHART 50

CUT-OFF, CONTROL AND SAFETY DEVICESEvery L.P.G. storage and supply system must be equipped with cut-off, safety,

control and measuring devices.

These consist of:

- cut-off valves

- check valves

- excess flow valves

- relief valves

- level indicators

- thermometers- p ressure gauges

- flow gauges

- filters

CUT-OFF VALVES

These are operated b y means of a hand-wheel or a lever.

They cut off the flow of liquid or gaseous L.P.G. They are normally installed along the

distribution network and upstream of each junction, in order to allow the flow to be cut off

in one or more sections of the network.Cut-off valves may be of different types depending on the shape of the shut-off

component: they may be flat seat, butterfly, ball valves, etc.

They must be checked (with soapy water) periodically to ensure that they are not

leaking to the outside, and the sealing component must be replaced if necessary.

- -

I/96


60/86

GAS


CHAPTER 3

CHART 51

CHECK VALVES

These ensure that the liquid or gas can only flow in one direction, and automatically

prevent any flow-back.

Fig. 5 - Check valve

EXCESS FLOW VALVES

They automatically cut off the flow of liquid or gaseous L.P.G. if leaks occur downstream

of the valve itself.

These valves are set at a specific flow-rate and pressure, and thus close when (and only

when) the flow-rate reaches or exceeds these setting values. This special feature must

be kept clearly in mind when choosing the type and characteristics of the valve. A valve

which shuts off at flow-rates only slightly above the normal operating flow-rate of the

plant on which it is installed might cause the troublesome and sometimes dangerous

prob lem of shutting down whenever a momentary higher flow-rate occurs, such as when

a shut-off valve downstream of the excess flow valve is opened too quickly. However,

if the excess flow valve is set too far above the operating flow-rates, it would become

less effective from the safety point of view in case of sudden L.P.G. leaks; above

certain limits, the valve might not shut even if pipes are comp letely cut through.

Only experience and the advice of skilled installation engineers will allow selection of the

right excess flow valve type and setting on each occasion.

I/96


61/86

GAS


CHAPTER 3

CHART 52

It must also be remembered that excess flow valves never shut totally, since evenwhen closed they allow a slight flow of liquid or gas to pass. This is in order to restore

the p ressure downstream of the valve after it has been shut, and this allow it to reopen

after a reasonably short time (about 15-20 seconds) as soon as the cause of its closure

is eliminated.

Excess flow valves are normally installed on the tank inlet or outlet points, and in all

points on the distribution network here p rotection against sudden or unexpected gas or

liquid leaks is necessary.

Fig. 6 - Excess flow valve

RELIEF VALVES

These are installed to p revent the p ressure in the various elements in an L.P.G. system

(tanks, pipelines, vaporizers, etc.) from exceeding specific limits, with serious risk of

damage (even explosion).

This excess pressure may occur for various causes:

- overfilling of the tank (since the liquid occupies all the space inside, leaving no room for

the gaseous cushion, it generates a hydrostatic pressure which will assume very high,

certainly dangerous values in case of even slight rises in ambient temperature). The

maximum permitted filling level is 85%.

I/96


62/86

GAS


CHAPTER 3

CHART 53

- prolonged exposure to external heat sources (strong sunlight on tanks and p ipelines;excess heat supplied by a vaporizer after the thermostat has failed, etc.);

- fire in the immediate vicinity of the containers (already envisaged in the prev ious p oint,

but here even more serious).

In all the cases described above, the relief valves op en automatically to all the escape

of liquid or gaseous L.P.G., preventing the pressure in the system from rising further.

The relief valves most often used are the "spring-loaded plate" type; the "lever or

counterweight" typ e is also very widely used on medium or large sized tanks (50 m3or

over).Relief valves are set to start to discharge at the pressure of 18 Kg/cm2 (i.e. the

maximum pressure for which the tanks are approved). They close again automatically

when the pressure drops back below the setting value. However, because of the

inev itab le mechanical frictions during operation of the valves, they almost always re-

close at a pressure value slightly lower than the setting p oint.

The openings for passage of the fluid when the valve is open must be large enough to

allow enough L.P.G. to escape to prevent the p ressure rising to hazardous values. The

dimensions of the valves must therefore selected on the basis of the size of the tank or

the component to be p rotected.

The L.P.G. discharged b y relief valves must always be carried away to ensure that it

does not cause a further danger. For valves installed on tanks, it is generally sufficient to

discharge the gas into a "candle", while valves on vaporizers discharge outside the

booth.

Discharge directly into the atmosphere is only permitted for smaller valves protecting

small lengths of pipe.

Malfunction of safety valves may be caused by:

- inadequate installation or incorrect size;

- dirt on the closing seat or the p late;- error in calibration on installation;

- loss of calibration because of modifications of the mechanical prop erties of the sp ring

due to ageing of the material.

Valves must therefore b e checked whenever major maintenance work is carried out.

I/96


63/86


64/86

GAS


CHAPTER 3

CHART 55

STORAGE PLANT WITH MOVABLE CONTAINERS

A) BANKS IN OPERATION AND AS RESERVE

A number of portable containers (cylinders or drums) connected to a delivery manifold

make up a bank.

The delivery unit consists of two banks, suitably connected, with one in operation and

the other as reserve alternately.

When the gas in the bank in op eration runs out, the reserve b ank is put into op eration

automatically or by an op erator. If this takes p lace automatically, a signal is given so that

the operator can order and install rep lacement containers.

A delivery unit may deliver the gaseous or liquid phase from the manifolds; if the liquidphase is delivered, a vaporizer is installed.

Before the type of delivery unit is chosen, it is important to calculat

Documents

Technical Course Manual Basic Level En