Block 1 Module 2

7/29/2019 Block 1 Module 2

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Steam and the Organisation Module 1.2Block 1 Introduction

The Steam and Condensate Loop 1.2.1

Module 1.2

Steam and the Organisation


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The Steam and Condensate Loop

Steam and the Organisation Module 1.2

1.2.2

Block 1 Introduction

Steam and the Organisation

The benefits described are not of interest to all steam users. The benefits of steam, as a problemsolver, can be subdivided according to different viewpoints within a business. They are perceiveddifferently depending on whether you are a chief executive, a manager or at operating level.

The questions these people ask about steam are markedly different.

Chief executive

The highest level executive is concerned with the best energy transfer solution to meet the strategicand financial objectives of the organisation.

If a company installs a steam system or chooses to upgrade an existing system, a significant capitalinvestment is required, and the relationship with the system, and the system provider, will be longand involved.

Chief executives and senior management want answers to the following questions:

Q. What kind of capital investment does a steam system represent ?

A steam system requires only small bore pipes to satisfy a high heat requirement. It does notrequire costly pumps or balancing, and only two port valves are required.

This means the system is simpler and less expensive than,for example, a high temperature hot water system. Thehigh efficiency of steam plant means it is compact andmakes maximum use of space, something which is oftenat a premium within plant.

Furthermore, upgrading an existing steam system withthe latest boilers and controls typically represents 50%of the cost of removing it and replacing it with a

decentralised gas fired system.Q. How will the operating and maintenance costs ofa steam system affect overhead costs ?

Centralised boiler plant is highly efficient and can use low interruptible tariff fuel rates. The boilercan even be fuelled by waste, or form part of a state-of-the-art Combined Heat and Power plant.

Steam equipment typically enjoys a long life - figures of thirty years or more of low maintenancelife are quite usual.

Modern steam plant, from the boiler house to the steam using plant and back again, can be fullyautomated. This dramatically cuts the cost of manning the plant.

Sophisticated energy monitoring equipment will ensure that the plant remains energy efficientand has a low manning requirement.

All these factors in combination mean that a steam system enjoys a low lifetime cost.

Q. If a steam system is installed, how can the most use be made of it ?

Steam has a range of uses. It can be used for space heating of large areas, for complex processesand for sterilisation purposes.

Using a hospital as an example, steam is ideal because it can be generated centrally at highpressure, distributed over long distances and then reduced in pressure at the point of use. Thismeans that a single high pressure boiler can suit the needs of all applications around the hospital,for example, heating of wards, air humidification, cooking of food in large quantities and sterilisation

of equipment.

It is not as easy to cater for all these needs with a water system.

Fig. 1.2.1


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Q. What if needs change in the future ?

Steam systems are flexible and easy to add to. They can grow with the company and be altered tomeet changing business objectives.

Q. What does using steam say about the company ?

The use of steam is environmentally responsible. Companies continue to choose steam because it

is generated with high levels of fuel efficiency. Environmental controls are increasingly stringent,even to the extent that organisations have to consider the costs and methods of disposing of plantbefore it is installed. All these issues are considered during the design and manufacture of steamplant.

Management level

A manager will consider steam as something that will provide a solution to a management problem,as something that will benefit and add value to the business. The managers responsibility is toimplement initiatives ordered by senior executives. A manager would ask How will steamenable successful implementation of this task ?

Managers tend to be practical and focused on completing a task within a budget. They willchoose to use steam if they believe it will provide the greatest amount of practicality and expediency,at a reasonable cost.

They are less concerned with the mechanics of the steam system itself. A useful perspectivewould be that the manager is the person who wants the finished product, without necessarilywanting to know how the machinery that produces it is put together.

Managers need answers to the following questions:

Q. Will steam be right for the process ?

Steam serves many applications and uses. It has a high heat content and gives up its heat at aconstant temperature. It does not create a temperature gradient along the heat transfer surface,

unlike water and thermal oils, which means that it may provide more consistent product quality.As steam is a pure fluid, it can be injected directly into the product or made to surround theproduct being heated. The energy given to the process is easy to control using two port valves,due to the direct relationship between temperature and pressure.

Q. If a steam system is installed, how can the most use be made of it ?

Steam has a wide variety of uses. It can be used for space heating over large areas, and for manycomplex manufacturing processes.

On an operational level, condensate produced by a manufacturing process can be returned to

the boiler feedtank. This can significantly reduce the boiler fuel and water treatment costs, becausethe water is already treated and at a high temperature.

Lower pressure steam can also be produced from the condensate in a flash vessel, and used inlow pressure applications such as space heating.

Fig. 1.2.2


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1.2.4


Q. What does steam cost to produce ?

Water is plentiful and inexpensive, and steam boilers are highly efficient because they extract alarge proportion of the energy contained within the fuel. As mentioned previously, central boilerplant can take advantage of low interruptible fuel tariffs, something which is not possible fordecentralised gas systems which use a constant supply of premium rate fuel.

Flash steam and condensate can be recovered and returned to the boiler or used on low pressureapplications with minimal losses.

Steam use is easy to monitor using steam flowmeters and SCADA compatible products.

For real figures, see The cost of raising steam, later in this Module.

In terms of capital and operating costs, it was seen when answering the concerns of the chiefexecutive that steam plant can represent value for money in both areas.

Q. Is there enough installation space ?

The high rates of heat transfer enjoyed by steam means that the plant is smaller and more compactthan water or thermal oil plant. A typical modern steam to hot water heat exchanger packagerated to 1 200 kW occupies only 0.7 m floor space. Compare this to a hot water calorifier whichmay take up a large part of a plant room.

Q. Not wishing to think too much about this part of the process, can a total solution beprovided ?

Steam plant can be provided in the form of compact ready-to-install packages which are installed,commissioned and ready to operate within a very short period of time. They offer many years oftrouble-free operation and have a low lifetime cost.

Technical personnel /operatorsAt the operating level, the day-to-day efficiency and working life of individuals can be directlyaffected by the steam plant and the way in which it operates. These individuals want to know

that the plant is going to work, how well it will work, and the effect this will have on their timeand resources.

Technical personal/operators need answers to the following questions:

Q. Will it break down ?

A well designed and maintained steam plant should have no cause to break down. The mechanicsof the system are simple to understand and designed to minimise maintenance. It is not unusualfor items of steam plant to enjoy 30 or 40 years of trouble-free life.

Q. When maintenance is required, how easy is it ?

Modern steam plant is designed to facilitate rapid easy maintenance with minimum downtime.

The modern design of components is a benefit in this respect. For example, swivel connectorsteam traps can be replaced by undoing two bolts and slotting a new trap unit into place. Modernforged steam and condensate manifolds incorporate piston valves which can be maintainedin-line with a simple handheld tool.

Sophisticated monitoring systems target the components that really need maintenance, ratherthan allowing preventative maintenance to be carried out unnecessarily on working items ofplant. Control valve internals can simply be lifted out and changed in-line, and actuators can bereversed in the field. Mechanical pumps can be serviced, simply by removing a cover, which hasall the internals attached to it. Universal pipeline connectors allow steam traps to be replaced inminutes.


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An important point to note is that when maintenance of the system is required, a steam system iseasy to isolate and will drain rapidly, meaning that repairs can be quickly actioned. Any minorleaks that do occur are non-toxic. This is not always the case with liquid systems, which areslower and more costly to drain, and may include toxic or difficult to handle thermal fluids.

Q. Will it look after itself ?

A steam system requires maintenance just like any other important part of the plant, but thanksto todays modern steam plant design, manning and maintenance requirements and the lifetimecosts of the system are low. For example, modern boiler houses are fully automated. Feedwatertreatment and heating burner control, boiler water level, blowdown and alarm systems are allcarried out by automatic systems. The boiler can be left unmanned and only requires testing inaccordance with local regulations.

Similarly, the steam plant can be managed centrally using automatic controls, flowmetering andmonitoring systems. These can be integrated with a SCADA system.

Manning requirements are thus minimised.

Industries and processes which use steam:

Table 1.2.1 Steam users

Heavy users Medium users Light users

Food and drinks Heating and ventilating Electronics

Pharmaceuticals Cooking Horticulture

Oil refining Curing Air conditioning

Chemicals Chilling Humidifying

Plastics Fermenting

Pulp and paper Treating

Sugar refining Cleaning

Textiles Melting

Metal processing Baking

Rubber and tyres Drying

Shipbuilding

Power generation


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1.2.6


Interesting uses for steam:

o Shrink-wrapping meat.

o Depressing the caps on food jars.

o Exploding corn to make cornflakes.

o Dyeing tennis balls.

o Repairing underground pipes (steam is used to expand and seal a foam which has been pumpedinto the pipe. This forms a new lining for the pipe and seals any cracks).

o Keeping chocolate soft, so it can be pumped and moulded.

o Making drinks bottles look attractive but safe, for example tamper-proof, by heat shrinking afilm wrapper.

o Drying glue (heating both glue and materials to dry on a roll).

o Making condoms.

o Making bubble wrap.

o Peeling potatoes by the tonne (high pressure steam is injected into a vessel full of potatoes.Then it is quickly depressurised, drawing the skins off).

o Heating swimming pools.

o Making instant coffee, milk or cocoa powder.

o Moulding tyres.

o Ironing clothes.

o Making carpets.

o Corrugating cardboard.

o Ensuring a high quality paint finish on cars.

o Washing milk bottles.

o Washing beer kegs.

o Drying paper.

o Ensuring medicines and medical equipment are sterile.

o Cooking potato chips.

o Sterilising wheelchairs.

o Cooking pieces of food, for example seafood, evenly in a basket using injected steam for

heat, moisture and turbulence at the same time.

o Cooking large vats of food by direct injection or jacket heating.

and hundreds more.


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The cost of raising steam

In todays industry, the cost of supplying energy is of enormous interest. Table 1.2.2 showsprovisional industrial fuel prices for the United Kingdom, obtained from a recent Digest of UKEnergy Statistics, which were available in 2001.

Table 1.2.2 UK fuel prices - 2001 (provisional)

Fuel Size of consumer 2001Small 55.49

Coal ( per tonne) Medium 46.04

Large 33.85

Small 142.73

Heavy fuel oil ( per tonne) Medium 136.15

Large 119.54

Small 230.48

Gas oil ( per tonne) Medium 224.61

Large 204.30

Small 4.89

Electricity (pence per kWh) Medium 3.61

Large 2.76

Small 1.10

Gas (pence per kWh) Medium 0.98

Large 0.78

The cost of raising steam based on the above costsAll figures exclude the Climate Change Levy (which came into force in April 2001) although theoil prices do include hydrocarbon oil duty.

The cost of raising steam is based on the cost of raising one tonne (1 000 kg) of steam using thefuel types listed and average fuel cost figures.

Table 1.2.3 UK steam costs - 2001 (provisional)

FuelAverage unit

Unit of supplyCost of raising

cost () 1 000 kg of steam ()

Heavy (3 500 s) 0.074 0 Per litre 9.12

OilMedium oil (950 s) 0.091 8 Per litre 11.31

Light oil (210 s) 0.100 0 Per litre 12.32

Gas oil (35 s) 0.105 4 Per litre 12.99

Natural gasFirm 0.006 3 Per kWh 6.99

Interruptible 0.005 0 Per kWh 5.55

Coal 35.160 0 Per Tonne 3.72

Electricity 0.036 7 Per kWh 25.26


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Fig. 1.2.3

Boiler efficiency

A modern steam boiler will generally operate at an efficiency ofbetween 80 and 85%. Some distribution losses will be incurredin the pipework between the boiler and the process plantequipment, but for a system insulated to current standards, thisloss should not exceed 5% of the total heat content of the steam.

Heat can be recovered from blowdown, flash steam can be usedfor low pressure applications, and condensate is returned to theboiler feedtank. If an economiser is fitted in the boiler flue, theoverall efficiency of a centralised steam plant will be around 87%.

This is lower than the 100% efficiency realised with an electricheating system at the point of use, but the typical running costsfor the two systems should be compared. It is clear that thecheapest option is the centralised boiler plant, which can use alower, interruptible gas tariff rather than the full tariff gas orelectricity, essential for a point of use heating system. The overallefficiency of electricity generation at a power station is

approximately 30 to 35%, and this is reflected in the unit charges.

Components within the steam plant are also highly efficient. For example, steam traps only allowcondensate to drain from the plant, retaining valuable steam for the process. Flash steam fromthe condensate can be utilised for lower pressure processes with the assistance of a flash vessel.

The following pages introduce some real life examples of situations in which a steam userhad, initially, been poorly advised and/or had access to only poor quality or incompleteinformation relating to steam plant. In both cases, they almost made decisions which wouldhave been costly and certainly not in the best interests of their organisation.

Some identification details have been altered.

Case study: UK West Country hospital considers replacing their steam systemIn one real life situation in the mid 1990s, a hospital in the West of England considered replacingtheir aged steam system with a high temperature hot water system, using additional gas firedboilers to handle some loads. Although new steam systems are extremely modern and efficientin their design, older, neglected systems are sometimes encountered and this user needed totake a decision either to update or replace the system.

The financial allocation to the project was 2.57 million over three years, covering professionalfees plus VAT.

It was shown, in consultation with the hospital, that only 1.2 million spent over ten yearswould provide renewal of the steam boilers, pipework and a large number of calorifiers. It was

also clear that renewal of the steam system would require a much reduced professional input.In fact, moving to high temperature hot water (HTHW) would cost over 1.2 million morethan renewing the steam system.

The reasons the hospital initially gave for replacing the steam system were:

o With a HTHW system, it was thought that maintenance and operating costs would be lower.

o The existing steam plant, boilers and pipework needed replacing anyway.

Maintenance costs for the steam system were said to include insurance of calorifiers, steam trapmaintenance, reducing valves and water treatment plant, also replacement of condensate pipework.

Operating costs were said to include water treatment, make-up water, manning of the boilerhouse, and heat losses from calorifiers, blowdown and traps.

The approximate annual operating costs the hospital was using for HTHW versus steam, aregiven in the Table 1.2.4.


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Table 1.2.4 Operating costs

Utility Steam () HTHW ()

Fuel245 000 180 000

0 37 500

Attendance 57 000 0

Maintenance 77 000 40 000

Water treatment 8 000 0

Water 400 100Electricity 9 000 12 000

Spares 10 000 5 000

Total 406 400 274 600

Additional claims in favour of individual gas fired boilers were given as:

o No primary mains losses.

o Smaller replacement boilers.

o No stand-by fuel requirement.

The costings set out above made the HTHW system look like the more favourable option interms of operating costs.

The new HTHW system would cost 1 953 000 plus 274 600 per annum in operating andmaintenance costs. This, in effect, meant decommissioning a plant and replacing it at a cost inexcess of 2 million, to save just over 130 000 a year.

The following factors needed to be taken into account:

o The 130 000 saving using HTHW is derived from 406 400 - 274 600. The steam fuel costcan be reduced to the same level as for HTHW by using condensate return and flash steamrecovery. This would reduce the total by 65 000 to 341 400.

o The largest savings claimed were due to the elimination of manned boilers. However, modern

boiler houses are fully automated and there is no manning requirement.

o The 37 000 reduction in maintenance costs looked very optimistic considering that the HTHWsolution included the introduction of 16 new gas fired boilers, 4 new steam generators and9 new humidifiers. This would have brought a significant maintenance requirement.

o The steam generators and humidifiers had unaccounted for fuel requirements and watertreatment costs. The fuel would have been supplied at a premium rate to satisfy the claim thatstand-by fuel was not needed. In contrast, centralised steam boilers can utilise low costalternatives at interruptible tariff.

o The savings from lower mains heat losses (eliminated from mains-free gas fired boilers) wereminimal against the total costs involved, and actually offset by the need for fuel at premiumtariff.

o The proposal to change appeared entirely motivated by weariness with the supposed lowefficiency calorifiers however on closer inspection it can be demonstrated that steam towater calorifiers are 84% efficient, and the remaining 16% of heat contained in the condensatecan almost all be returned to the boiler house. Gas fired hot water boilers struggle to reach the84% efficiency level even at full- load. Unused heat is just sent up the stack. Hot water calorifiersare also much larger and more complicated, and the existing plant rooms were unlikely tohave much spare room.

o A fact given in favour of replacing the steam system was the high cost of condensate pipereplacement. This statement tells us that corrosion was taking place, of which the commonest

cause is dissolved gases, which can be removed physically or by chemical treatment. Removingthe system because of this is like replacing a car because the ashtrays are full !

o A disadvantage given for steam systems was the need for insurance inspection of steam/ water


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1.2.10


calorifiers. However, HTHW calorifiers also require inspection !

o A further disadvantage given was the need to maintain steam pressure reducing valves. Butwater systems contain three port valves with a significant maintenance requirement.

o The cost of make-up water and water treatment for steam systems was criticised. However,when a steam system requires maintenance, the relevant part can be easily isolated and quicklydrained with few losses (this minimises downtime). In contrast, a water system requires wholesections to be cooled and then drained off. It must then be refilled and purged of air aftermaintenance. HTHW systems also require chemical treatment, just like steam systems.

Presented with these explanations, the hospital realised that much of the evidence they had beenbasing their decision on was biased and incomplete. The hospital engineering team reassessedthe case, and decided to retain their steam plant and bring it up to date with modern controls andequipment, saving a considerable amount of money.

Trace heating

Trace heating is a vital element in the reliable operation of pipelines and storage/process vessels,across a broad range of industries.

A steam tracer is a small steam pipe which runs along the outer surface of a (usually) larger processpipe. Heat conductive paste is often used between the tracer and the process pipe. The two pipesare then insulated together. The heat provided from the tracer (by conduction) prevents the contentsof the larger process pipe from freezing (anti-frost protection for water lines) or maintains thetemperature of the process fluid so that it remains easy to pump.

Tracing is commonly found in the oil and petrochemical industries, but also in the food andpharmaceutical sectors, for oils, fats and glucose. Many of these fluids can only be pumped attemperatures well above ambient. In chemical processing, a range of products from acetic acidthrough to asphalt, sulphur and zinc compounds may only be moved through pipes if maintainedat a suitable temperature.

For the extensive pipe runs found in much of process industry, steam tracing remains the mostpopular choice. For very short runs or where no steam supply is available, electrical tracing isoften chosen, although hot water is also used for low temperature requirements. The relativebenefits of steam and electric tracing are summarised in Table 1.2.5.

Table 1.2.5 The relative merits of steam and electric trace heating

Steam Electric

trace heating trace heating

Robustness - ability to resist adverse weather and physical abuse Good Poor

Flexibility - ability to meet demands of different products Excellent Poor

Safety - suitability for use in hazardous areas Excellent Cannot be used in all zones

Energy costs per GJ 0 to 2.14 8.64System life Long Limited

Reliability High High

Ease by which the system can be extended Easy Difficult

Temperature control - accuracy of maintaining temperature Very good /high Excellent

Suitability for large plant Excellent Moderate

Suitability for small plant Moderate Good

Ease of tracer installation Moderate Requires specialist skills

Cost of maintenance Low Moderate

Specialised maintenance staff requirement No Yes

Availability as turnkey project Yes Yes

Case study: UK oil refinery uses steam tracing for 4 km pipeline


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In 1998, a steam trace heating system was installed at one of the UKs largest oil refineries.

BackgroundThe oil company in question is involved in the export of a type of wax product. The wax hasmany uses, such as insulation in electric cabling, as a resin in corrugated paper and as a coatingused to protect fresh fruit.

The wax has similar properties to candle wax. To enable it to be transported any distance in theform of a liquid, it needs to be maintained at a certain temperature. The refinery therefore requireda pipeline with critical tracing.

The project required the installation of a 200 mm diameter product pipeline, which would runfrom a tank farm to a marine terminal out at sea a pipeline of some 4 km in length.

The project began in April 1997, installation was completed in August 1998, and the first successfulexport of wax took place a month later.

Although the refinery management team was originally committed to an electric trace solution,they were persuaded to look at comparative design proposals and costings for both electric andsteam trace options.

The wax applicationThe key parameter for this critical tracing application was to provide tight temperature control ofthe product at 80C, but to have the ability to raise the temperature to 90C for start-up orre-flow conditions. Other critical factors included the fact that the product would solidify attemperatures below 60C, and spoil if subjected to temperatures above 120C.

Steam was available on site at 9 bar g and 180 C, which immediately presented problems ofexcessive surface temperatures if conventional schedule 80 carbon steel trace pipework were tobe used. This had been proposed by the contractor as a traditional steam trace solution for the oilcompany.

The total tracer tube length required was 11.5 km, meaning that the installation of carbon steel

pipework would be very labour intensive, expensive and impractical. With all the joints involvedit was not an attractive option.

However, todays steam tracing systems are highly advanced technologically. Spirax Sarcoandtheir partner on the project, a specialist tracing firm, were able to propose two parallel runs ofinsulated copper tracer tube, which effectively put a layer of insulation between the product pipeand the steam tracer. This enabled the use of steam supply at 9 bar g, without the potential forhot spots which could exceed the critical 120C product limitation.

The installation benefit was that as the annealed ductile steam tracer tubing used was available incontinuous drum lengths, the proposed 50 m runs would have a limited number of joints, reducingthe potential for future leaks from connectors.

This provided a reliable, low maintenance solution.

After comprehensive energy audit calculations, and the production of schematic installationdrawings for costing purposes, together with some careful engineering, the proposal was to usethe existing 9 bar g distribution system with 15 mm carbon steel pipework to feed the tracingsystem, together with strainers and temperature controls. Carbon steel condensate pipework wasused together with lightweight tracing traps which minimised the need for substantial fabricatedsupports.

The typical tracer runs would be 50 m of twin isolated copper tracer tubing, installed at the 4 and8 oclock positions around the product pipe, held to the product pipeline with stainless steelstrap banding at 300 mm intervals.

The material and installation costs for steam trace heating were about 30% less than the electric


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1.2.12


tracing option. In addition, ongoing running costs for the steam system would be a fraction ofthose for the electrical option.

Before the oil company management would commit themselves to a steam tracing system, theynot only required an extended product warranty and a plant performance guarantee, but alsoinsisted that a test rig should be built to prove the suitability of the self- acting controlled tracer forsuch an arduous application.

Spirax Sarco were able to assure them of the suitability of the design by referral to an existinginstallation elsewhere on their plant, where ten self-acting controllers were already installed andsuccessfully working on the trace heating of pump transfer lines.

The oil company was then convinced of the benefits of steam tracing the wax product line andwent on to install a steam tracing system.

Further in-depth surveys of the 4 km pipeline route were undertaken to enable full installationdrawings to be produced. The company was also provided with on-site training for personnel oncorrect practices and installation procedures.

After installation the heat load design was confirmed and the product was maintained at the

Fig. 1.2.4

Lagging

Wax

Steam

required 80C.

The oil company executives were impressed with the success of the project and chose to installsteam tracing for another 300 m long wax product line in preference to electric tracing, eventhough they were initially convinced that electric tracing was the only solution for criticalapplications.


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Questions

1. How does the cost of upgrading a steam system compare with installing a decentralisedgas fired system ?

a| It costs the same to upgrade the steam system.

b| It costs twice as much to upgrade the steam system.

c| It costs 75% as much to upgrade the steam system.

d| It costs half as much to upgrade the steam system.

2. Which of the following uses for steam could be found in a hospital ?

a| Space heating.

b| Sterilisation.

c| Cooking.

d| All of the above.

3. Which of the following statements is true ?

a| Steam creates a temperature gradient along the heat transfer surface,ensuring consistent product quality.

b| Steam gives up its heat at a constant temperature without a gradient along theheat transfer surface, ensuring consistent product quality.

c| High temperature oils offer a constant temperature along theheat transfer surface, which leads to poor product quality.

d| High temperature oils can be directly injected into the product to be heated.

4. A hot water calorifier can occupy much of a plant room. How much floor space does amodern steam to hot water packaged unit need if it is rated at 1200 kW ?

a| 0.7 m

b| 7.0 m

c| 1.2 m

d| 12 m

5. Why is steam inexpensive to produce ?

a| Steam boilers can use a variety of fuels.

b| Steam boilers can utilise the heat from returned condensate.

c| Steam boilers can be automated.

d| All of the above.

6. Which of the following statements best describes steam tracing ?

a| Steam is injected into the process pipe to keep the contents moving.

b| An electric jacket is used to heat the process piping.

c| A steam tracer is a small steam pipe which runs along the outside of a process pipe.

d| A tracer is a small water filled pipe which runs along the outside of a process pipe.

1:c,2:d,3:b,4:a,5:d,6:cAnswers


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