Optimization of a CHP plant
Introduction
An environmental charge on emissions of nitrogen oxides (NOx) has created a
strong incentive for optimization of many combustion plants in Sweden. We have
successfully used sequential simplex optimization as a tool in this work. Here is a brief
description of one such project.
The starting conditions
The assignment was to optimize a 100 MW combined heat and power (CHP) plant burning a
mixture of bio fuel and oil. The CHP plant was equipped with low-NOx burners
and the emission level of NOx was 85-95 mg/MJ. Four variables were selected for
optimization: Secondary air at two levels, distribution of burner air and distribution of
fuel between burners. The two response variables to be optimized were the NOx-emission
and the combustion conditions. The latter variable was based on both measurements and
observations. The response variables were combined into one joint response using a fuzzy
set approach.
Optimization trials
We calculated the optimization trials using the modified simplex method. 16 trials were
required to cut the NOx-emission down to 60-65 mg/MJ while maintaining good
combustion conditions.
Profit
This 25% reduction can easily be converted into an economic profit, since the
environmental charge is set to SEK 40 for each kg of NOx. The saving from this
optimization is 450 SEK/h, and with 5000 h of operation this converts to a roughly SEK
2,200,000 (USD 275,000) per year.
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