Psce 2011 Article final

Data 
Value 
Unit 
Gross Electric Power 
105 
MW 
Sugarcane milling 
17000 
T/day 
Ethanol production 
1800 
m³/day 
High Pressure (abs) 
101 
Bar 
Medium Pressure – extraction (abs) 
17 
Bar 
Low Pressure – process (abs) 
2,5 
Bar 
Electricity production 
80 
MWe 
Electricity aux. consumption 
10 
MWe 
MP turbine consumption 
4 
MW 
Escape Steam flow from BPSTGs 
383 
T/h 
Escape Steam flow from TPs 
36.4 
T/h 
Steam flow from Conditioning Valve
0.6 
T/h 
Escape Steam Loss 
10.7 
T/h 
Escape Steam Temperature 
126.8 
ºC 
Escape Steam Pressure (abs) 
2.4 
Bar 
Escape Steam Enthalpy 
2715.7 
kJ/kg 
Escape Condensate Temperature 
123 
ºC 
Escape Condensate Pressure 
2.18 
bar 
Escape Condensate Enthalpy 
516.564 
kJ/kg 
Bagasse LHV 
7578.5 
kJ/kg 
Boiler bagasse consumption 
181681 
kg/h 
Useful Mechanical/Electrical Work 
74000 
kWh/h 
Useful Heat 
250029.5 
kWh/h 
Fuel Energy 
382463 
kWh/h 
FUE
t
 
84.72 
% 
Premise 2 – for 
temperature, 
pressure 
and 
flow 
measurements, it is assumed the average parameter value 
integrated in a one second time base. It means that for each 
one second there is a heat calculation for each stream. Thus, 
the one second time based calculated operational heat values 
are integrated for the average one hour time based heat in each 
flow. This premise is important to obtain a better accuracy for 
the operational heat. 
Premise 3 – for process input, the escape steam condition 
is saturated with title equals 1. 
Premise 4 – for process output, the escape condensate 
condition is no steam title.
Premise 5 – although every CHP plant has a steam 
conditioning valve for turbo-generation by-pass, in regular 
conditions it is considered closed, with flow equals zero. 
Premise 6 – there is no loss of mass in the flow through 
each turbine. 
Premise 7 – the process for a biomass cogeneration 
system is simplified as having one single stream.
Premise 8 – the lost energy due to loss of mass in the 
stream through the process is derived from the specific 
enthalpy of steam on the process input. 
2)
 
Work – Electrical / Mechanical 
The work is the most simple parameter to measure in power 

---

5 
plants because it is directly available in one single metering 
device per stream.
The generated electricity can be measured by power 
meters. In order to comply with regulatory standards that are 
common to many countries, power meters are used so for 
gross energy metering as for energy export metering in power 
plants.
The auxiliary systems electricity consumption can be 
measured using so power meters as protection relays. The 
usual cogeneration auxiliary systems to have measured 
consumption are: 
-
Boiler Auxiliary Substation; 
-
Power house Auxiliary Substation; 
-
Bagasse conveyor system Auxiliary Substation; 
-
Cooling towers Auxiliary Substation; and 
-
Water utility Auxiliary Substation. 
The mechanical work from machines like boiler feedwater 
pumps or milling turbines can be measured by instantaneous 
power lecture available on its controller. 
This way, the accumulated kWh in a period of one hour can 
be measured and transmitted via a device communication port 
from each power meter, protection relay or controller, to the 
established database server. 
3)
 
Heat 
The heat measurement is obtained by indirect mean. It is 
done after lecture and handle over temperature, pressure and 
flow data from input and output points on the process stream. 
After measured and integrated in the time base, the values of 
these parameters are then used for operational heat calculation 
through the same equations as stated above.
Referring to the PFD of Fig. 1, the ideal place for the 
instruments that would permit to better measure steam and 
condensate enthalpy, that represents heat, is the line right 
before the process input and the line right after it. However, 
the most usual place to have temperature, pressure and flow 
transmitters that permit to calculate escape steam enthalpy are 
installed on the pipes between turbine escapes and low 
pressure steam header. It means that the escape steam enthalpy 
entering the process is a sum of the ones escaping from the 
steam turbines as detailed in (7).
(7) 
where: 
= Turbine generator mass flow, in kg/s. 
h
ES
= Escape steam specific enthalpy, in kJ/kg, as derived 
from steam temperature and pressure. 
= Turbine machine mass flow, in kg/s. 
After calculating the average 
value per second, a one 
hour time based average can be then obtained. 
The condensed water enthalpy from the process is quite 
complex to obtain. The usual place for temperature and 
pressure transmitters is the escape condensate tank right 
before condensate pumps that will push it back to the boiler 
deaerator. The usual place for escape condensate flow 
transmitter is the line right after the same condensate pumps to 
deaerator. 
Therefore, the escape condensate transferred heat can be 
calculated as detailed in (8).
(8) 
where: 
= Escape condensate from process output mass flow, in 
kg/s. 
h
CE
= Escape steam specific enthalpy, in kJ/kg, as derived 
from condensate temperature and pressure. 
The steam losses heat can be calculated as detailed in (9).
(9) 
where: 
= Turbine generator mass flow, in kg/s. 
= Turbine machine mass flow, in kg/s. 
= Escape condensate from process output mass flow, in 
kg/s. 
h
ES
= Escape steam specific enthalpy, in kJ/kg, as derived 
from steam temperature and pressure. 
It is important to notice that the heat loss is derived from 
the mass loss considered as escape steam enthalpy condition. 
There are some other important considerations to be done at 
this point. The here stated places for temperature, pressure and 
flow transmitters are not general rule. For each cogeneration 
in which the proposed methodology is applied, the 
measurement points must be verified as well as eventual 
adaptations to the stated equations must be made. In order to 
minimize that risk, the parameters defined in this methodology 
are as general as possible in order to attend most of the 
applications. Moreover, some of the instruments usually found 
in cogeneration plants are not transmitters, what requires 
manual measurement procedures. For a totally automatic 
measurement system implementation, verifications and 
eventual instrument changes must be done. Far from being a 
technical issue, this requirement is just a matter of 
instrumentation cost which is perfectly possible to meet by the 
owner. 
4)
 
Fuel 
The transferred fuel energy measurement is a challenging