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
AMMONIA PLANT OSBL
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
D
072feed
M
M
100
x
1VVV 





−−=

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
D
072fuel
M
M
100
x
1VVV 





−−=
with:
test period
Vfuel actual fuel consumption for 72 hours

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
D
072flare
M
M
100
x
1VVV 





−−=
with:
test period
Vfuel actual fuel consumption for 72 hours
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
1
urea,flareflare3
2
3NH,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
( ) 





−−=
100
x
1VVV 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
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
1I
i,WPD36
1
in,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
( ) 





−−−=
100
x
1VVV 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
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
1I
i,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
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
D
02i
100
x
1mmm
ρ
ρ






−−=

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
1I
i,2CO,steami,in,steam36
1
out,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:
( ) 





−−=
100
x
1mmm 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
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
1I
i36
1
in,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:
( ) 





−−=
100
x
1PPP 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)
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).
( ) 





−−=
100
x
1PPP 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

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
g 424 °C
MP steam to FMD_002
A/B
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
D
02i
100
x
1mmm
ρ
ρ






−−=

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
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
1I
iU,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.
( ) 





−−=
100
x
1PPP 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
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 %
•

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
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

Calculation of an Ammonia Plant Energy Consumption:

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