Calculation of an Ammonia Plant Energy Consumption:

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Calculation of an Ammonia Plant Energy Consumption: Case Study: #06023300 Plant Note Book Series: PNBS-0602

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CALCULATION OF 3300 T/D ACME AMMONIA PLANT ENERGY CONSUMPTION Case Study: #06023300 CONTENTS 0 SCOPE 1 CALCULATION OF NATURAL GAS PROCESS FEED CONSUMPTION 2 CALCULATION OF NATURAL GAS PROCESS FUEL CONSUMPTION 3 CALCULATION OF NATURAL GAS CONSUMPTION FOR PILOT BURNERS OF FLARES 4 CALCULATION OF DEMIN. WATER FROM DEMIN. UNIT 5 CALCULATION OF DEMIN. WATER TO PACKAGE BOILERS 6 CALCULATION OF MP STEAM EXPORT 7 CALCULATION OF LP STEAM IMPORT 8 DETERMINATION OF ELECTRIC POWER CONSUMPTION 9 DETERMINATION OF THE TOTAL ENERGY CONSUMPTION OF THE AMMONIA PLANT ISBL 10 ADJUSTMENT OF ELECTRIC POWER CONSUMPTION FOR TEST RUN CONDITIONS 11 CALCULATION OF AMMONIA SHARE IN MP STEAM CONSUMPTION IN UTILITIES 12 CALCULATION OF AMMONIA SHARE IN ELECTRIC POWER CONSUMPTION IN UTILITIES 13 DETERMINATION OF THE TOTAL ENERGY CONSUMPTION OF THE AMMONIA PLANT OSBL 14 DETERMINATION OF THE TOTAL ENERGY CONSUMPTION OF THE AMMONIA PLANT



CALCULATION OF 3300 T/D ACME AMMONIA PLANT ENERGY CONSUMPTION 0 SCOPE The 3300 t/d ACME ammonia plant energy consumption shall be calculated based on the measurements for import and export of process and utility streams and electric power related to the ammonia production listed below, for a test period of 72 hours. Note: (ISBL) inside battery limits and (OSBL) outside battery limits Streams Considered Ammonia product Process Feed Process Fuel Fuel for Flares MP steam export for utilities LP steam import from boiler BFW/FD turbine Demin. water in Demin. Water out 1 CALCULATION OF NATURAL GAS PROCESS FEED CONSUMPTION DCS indication of the flow measurement for natural gas feed consumption is based on the following composition as per Design Basis. CH4 87.5%

The natural gas composition during shall be used to determine molecular weight and heating value of the gas. For molecular weights and heating values of the individual components refer to GBHE_ PNBS-0601. The influence of the instrument tolerance and the different molecular weight on the orifice flow meter shall be accounted for by:

( )i

D072feed M

M100

x1VVV

−−=



with:

MD design value for molecular mass of natural gas (xxx kg/kmol as per Design Basis) Mi actual molecular weight of natural gas V0 reading from flow meter at the beginning of the 72-hour test period V72 reading from flow meter at the end of the 72-hour period Vfeed actual feed consumption for 72 hours x tolerance of flow meter

2 CALCULATION OF NATURAL GAS PROCESS FUEL CONSUMPTION:

The same gas specified under (1) is also used as reformer fuel. For the same reasons as given above it might be necessary to correct the measured flow by the actual molecular weight. For the time of the performance test, a totalizer flow meter will be added to the existing flow meter in the DCS. Total consumption then is calculated by:

( )i

D072fuel M

M100

x1VVV

−−=

with:

MD design value for molecular mass of natural gas (xxx kg/kmol as per Design Basis) Mi actual molecular weight of natural gas V0 reading from flow meter at the beginning of the 72-hour test period V72 reading from flow meter at the end of the 72-hour period Vfuel actual fuel consumption for 72 hours x tolerance of flow meter



3 CALCULATION OF NATURAL GAS CONSUMPTION FOR PILOT BURNERS OF FLARES:

The same gas specified under (1) is also used as fuel for the pilot burners of the flares. For the same reasons as given above it might be necessary to correct the measured flow by the actual molecular weight. For the time of the test period, a totalizer flow meter will be added to the existing Flow Meter in the DCS. Total consumption then is calculated by:

( )i

D072flare M

M100

x1VVV

−−=

with:

MD design value for molecular mass of natural gas (xxx kg/kmol as per Design Basis) Mi actual molecular weight of natural gas V0 reading from flow meter at the beginning of the 72-hour test period V72 reading from flow meter at the end of the 72-hour period Vfuel actual fuel consumption for 72 hours x tolerance of flow meter

As the fuel goes to two flares in the ammonia plant (syngas and ammonia) and one belonging to the urea plant, the individual shares are allocated as follows: flare3

1urea,flareflare3

23NH,flare VV,VV ==

4 CALCULATION OF DEMIN. WATER FROM DEMIN. UNIT:

Import of demin. water to the ammonia plant is measured at orifice flow meter. For the time of the test period, a totalizer will be added in the DCS. Temperature for enthalpy calculation is taken from the designated TI.



As temperature might vary over the course of time, enthalpy shall be calculated separately for each 2-hour-period by hVhmH i,WPDi ρ== where density ρ and specific enthalpy h are calculated as function of temperature and pressure using VDI steam tables. Temperature reading shall be done at the end of each 2-hour interval. The demin water flow in the interval is calculated as

( )

−−=

100x1VVV 0,WPD2,WPDi,WPD

with:

VWPD,0 reading from the flow meter at the beginning of the 2-hour time interval VWPD,2 reading from the flow meter at the end of the 2-hour time interval VWPD,i actual demin. water consumption for the 2-hour time interval x tolerance of the flow meter

Temperature for enthalpy calculation is taken from the designated TI. Pressure is taken as 7 bar abs. fixed HOLD for this purpose as density and enthalpy both are not significantly depending on the actual pressure in the region of interest. Temperature tolerance of the designated TI is neglected. Total enthalpy flow to the plant over the 72-hour period of the test period is then

∑=

=36

1Ii,WPD36

1in,WPD HH



5 CALCULATION OF DEMIN. WATER TO PACKAGE BOILERS Export of preheated demin. water to utilities is measured at the designated orifice flow meter with the totalizer flow meter. Temperature for enthalpy calculation is taken from the designated TI. As temperature might vary over the course of time, enthalpy shall be calculated separately for each 2-hour-period by iii,WPDiii hVhmH ρ== where density ρi and specific enthalpy hi are calculated as function of temperature and pressure using VDI steam tables. Temperature reading shall be done at the end of each 2-hour interval. The demin water flow in the interval is calculated as

( )

−−−=

100x1VVV 0,WPD2,WPDi,WPD

with:

VWPD,0 reading from the designated flow meter at the beginning of the 2-hour time interval VWPD,2 reading from the designated flow meter at the end of the 2-hour time interval VWPD,i actual demin. water export for the 2-hour time interval (negative because it is export) x tolerance of the designated flow meter

Temperature for enthalpy calculation is taken from the designated TI. Pressure is taken as 6 bar abs. fixed HOLD as return pressure from the ammonia plant for this purpose as density and enthalpy both are not significantly depending on the actual pressure in the region of interest. Temperature tolerance of the designated TI is neglected. Total enthalpy export from the ammonia plant over the 72-hour period of the performance test run is then

∑=

=36

1Ii,WPDout,WPD HH



6 Calculation of MP steam export:

MP steam export is determined as the difference MP steam import to ammonia area – MP steam consumption of CO2 compressor turbine MP steam export from ammonia plant According to this definition, export (outbound flow) shall carry negative sign. For the time of the test period, totalizers FMD_002 flow meter and compressor turbine flow meter shall be added to the existing indications in the DCS. As temperature might vary over the course of time, enthalpy for both streams shall be calculated separately for each 2-hour-period by iii hmH = where specific enthalpy hi is calculated as function of temperature and pressure using VDI steam tables.

Flow

measurement Pressure

measurement Temperature measurement

MP steam import to ammonia area

FMD_001 PMD- 01 A/B TI_001

– design conditions 52 kg/cm2 g 424 °C MP steam consumption of CO2 compr. turb.

FMD_002 PMD_02 TI_002

– design conditions 52 kg/cm2 g 424 °C

Specific enthalpy under design conditions is h = 3253 kJ/kg. Temperature reading shall be done at the end of each 2-hour interval. The steam flows in the interval are calculated as below. As FMD_001 and FMD_002 are not compensated by temperature and pressure this shall be done using the following formula, when temperature and pressure are off the above mentioned design conditions:

( )i

D02i 100

x1mmmρρ

−−=



with:

ρD design value for steam density (17.25 kg/m3) ρi actual steam density as function of pressure and temperature by steam table m0 reading from FMD_001 / FMD_002 at the beginning of the 2-hour period m2 reading from FMD_001 / FMD_002 at the end of the 2- hour period mi actual steam flow for 2 hours x tolerance of FMD_001 / FMD_002

Temperatures and pressures for the enthalpy calculation are taken from the above table. Tolerance of temperature and pressure measurements are neglected. Total enthalpy of MP steam export from the ammonia plant over the 72-hour period of the test period is then

( )∑=

−=36

1Ii,2CO,steami,in,steam36

1out,steam HHH

7 CALCULATION OF LP STEAM IMPORT

LP steam import is from utilities to the ammonia plant is measured at the designated flow meters. Its DCS indication is corrected by pressure and temperature. For the time of the test period, a totalizer shall be added to the existing indication in the DCS. As steam conditions might vary over the course of time, enthalpy for the stream shall be calculated separately for each 2-hour-period by

iii hmH =

where specific enthalpy hi is calculated as function of pressure and temperature using VDI steam tables. Pressure and temperature readings shall be done at the end of each 2-hour interval. Specific enthalpy under design conditions (p = 4.0 kg/cm2 g, T = 252 °C) is h = 2966 kJ/kg.



Tolerance of pressure and temperature measurements are neglected. The steam flow in the interval is calculated by:

( )

−−=

100x1mmm 02i

with:

m0 reading from the designated flow meter at the beginning of the 2-hour period m2 reading from the designated flow meter at the end of the 2- hour period mi actual steam flow for 2 hours x tolerance of the designated flow meter Total enthalpy of LP steam import from the ammonia plant over the 72-hour test period is then

∑=

=36

1Ii36

1in,steam HH

8 DETERMINATION OF ELECTRIC POWER CONSUMPTION The electric power consumption taken from the watt-hour meters for units 411 to 419 shall be added up. • For medium-voltage consumers these are marked by "+" in column in the

Table "Metering of medium-voltage motors" (in total 9 motors). Individual readings can be taken for each consumer.

• For low-voltage consumers these are marked by "+" in column of Table "Metering of low-voltage switchgears and MCC" . Readings can be taken from the receiving feeders for each switchgear. Individual consumers marked by "–" have to be subtracted by individual metering.



Summing all up, the tolerance of the measuring devices shall be considered as follows:

( )

−−=

100x1PPP 072

with: P0 sum of all relevant watt-hour meters at the beginning of the 72-hour period P72 sum of all relevant watt-hour meters at the end of the 72- hour period P actual consumption figure for 72 hours

x tolerance of watt-hour meters (which is HOLD)

9 DETERMINATION OF THE TOTAL ENERGY CONSUMPTION OF THE AMMONIA PLANT ISBL

The contributions from (1) to (8) are converted into energy equivalents of consumed natural gas, then set into relation to the total ammonia production mt and are then summed up. As the energy equivalent of the natural gas flows, the higher heating value (HHV) is calculated from the natural gas composition as per (1) using to the table in GBHE_PNBS-0601, "Calculation of Caloric Value and other Characteristic Data of Fuel Gas". Steam and water streams are converted into their energy equivalents as described earlier. Electric power measured in kWh is converted in kcal by the fixed conversion factor.

1 KWh = 2885 kcal/kWh = 12.026 MJ/kWh



Total energy consumption inside battery limits (ISBL) is: natural gas for process feed (1) × HHV / mt + natural gas for process fuel (2) × HHV / mt + natural gas for flares (3) × HHV / mt + demin. water from demin. unit (4) / ηB × HHV/LHV / mt + demin. water to pack. boilers (5) / ηB × HHV/LHV / mt + MP steam export (6) / ηB × HHV/LHV / mt + LP steam import (7) / ηB × HHV/LHV / mt + electric power consumption (8) × 2885 kcal/kWh / mt = E ISBL = specific energy consumption per ton of ammonia inside battery limits

10 ADJUSTMENT OF ELECTRIC POWER CONSUMPTION FOR TEST PERIOD CONDITIONS: According to the description in paragraph (8), the electric power consumption taken from the watt-hour meters for

• Designated A/B transfer pumps to storage (low voltage)

• Designated A/B storage refrigeration compressor (medium voltage) has to be added up. Readings shall be taken from the MCC (low voltage) and from the switchgear (medium voltage).

( )

−−=

100x1PPP 072

with: P0 sum of the watt-hour meters at the beginning of the 72-hour period P72 sum of the watt-hour meters at the end of the 72-hour period P actual consumption figure for 72 hours x tolerance of watt-hour meters (which is HOLD)



11 CALCULATION OF AMMONIA SHARE IN MP STEAM CONSUMPTION

IN UTILITIES The share of the ammonia plant in the MP steam consumption of

• designated seawater circulation pump turbines A/B, measured at FI_001

• designated closed loop circulation pump turbines A/B, measured at FI_002 is calculated. For the time of the test period, designated totalizer(s) flow meters shall be added to the existing indications in the DCS. As temperature might vary over the course of time, enthalpy for both streams shall be calculated separately for each 2-hour-period by iii hmH = where specific enthalpy hi is calculated as function of temperature and pressure using VDI steam tables. These readings shall be taken from:

Flow measuremen

t

Pressure measuremen

t

Temperature measurement

MP steam to FMD_001 A/B

– design conditions 52 kg/cm2 g 424 °C MP steam to FMD_002 A/B

– design conditions 52 kg/cm2 g 424 °C Specific enthalpy under design conditions is h = 3253 kJ/kg. Temperature reading shall be done at the end of each 2-hour interval. The steam flows in the interval are calculated as below. As the designated flow meters are not compensated by temperature and pressure this shall be done using the following formula, when temperature and pressure are off the above mentioned design conditions:

( )i

D02i 100

x1mmmρρ

−−=



with:

ρD design value for steam density (17.25 kg/m3) ρi actual steam density as function of pressure and temperature by steam table m0 reading from the designated flow meters at the beginning of the 2-hour period m2 reading from the designated flow meters at the end of the 2- hour period mi actual steam flow for 2 hours x tolerance of the designated flow meters

Temperatures and pressures for the enthalpy calculation are taken from the above table. Tolerance of temperature and pressure measurements are neglected.

Total enthalpy of MP steam for each of the consumers over the 72-hour test period is then

∑=

=36

1IiU,t HH , U = 435, 436

The share of the ammonia plant in this enthalpy is obtained by multiplication with the appropriate factor fU for the respective utility unit H435 = Ht,435 f435 , H436 = Ht,436 f436 with:

• seawater pumps: f435 = 70 % • closed loop pumps: f436 = 52 %



12 CALCULATION OF AMMONIA SHARE IN ELECTRIC POWER CONSUMPTION IN UTILITIES

The electric power consumption of the following utility units has to be considered in the ammonia plant consumption figure.

• designated polished water pumps

• designated cooling tower fans and seawater make-up pump The readings of the respective watt-hour meters in the MCC (all low voltage) have to be added up.

( )

−−=

100x1PPP 072t

with: P0 sum of the watt-hour meters at the beginning of the 72-hour period P72 sum of the watt-hour meters at the end of the 72-hour period Pt actual consumption figure for 72 hours x tolerance of watt-hour meters (which is HOLD) The share of the ammonia plant in these powers is obtained by multiplication with the appropriate factor fU for the respective utility unit P433 = Pt,433 f433 , P435 = Ht,435 f435 with: • polished water pumps: f433 = 75 % • cooling tower and seawater pumps: f435 = 70 % •



13 DETERMINATION OF THE TOTAL ENERGY CONSUMPTION OF THE AMMONIA PLANT OSBL

The contributions from (10) to (12) are converted into energy equivalents of consumed natural gas, then set into relation to the total ammonia production mt and are then summed up, same as in paragraph (9) above. Total energy consumption outside battery limits (OSBL) is:

electric power transfer pumps (k) × 2885 kcal/kWh / mt + electric power storage refr. (k) × 2885 kcal/kWh / mt + MP steam sea water (l) x f435 / ηB × HHV/LHV / mt + MP steam closed loop (l) x f436 / ηB × HHV/LHV / mt + electric power pol. w. (m) x f433 × 2885 kcal/kWh / mt + electric power CT (m) x f435 × 2885 kcal/kWh / mt = E OSBL = specific energy consumption per ton of ammonia outside battery limits 14 DETERMINATION OF THE TOTAL ENERGY CONSUMPTION OF THE AMMONIA PLANT

The contributions from ISBL (9) and OSBL (13) are added. Total energy consumption is E = EISBL + EOSBL Guaranteed value: 8.34 Gcal / t

