| OCR Text |
Show 10 3.5 HEAT RECOVERY ALLOWANCE While the basic emission target for shaft or electrical power output is determined by the Power Output Allowance, an additional Heat Recovery Allowace (HRA) was established to recognize the environmental benefits of increased energy efficiency. It allows the turbine to be credited with NO emissions saved from other combustion sources if it can be demo~strated that useful energy is to be recovered during normal operation from the facility's exhaust thermal energy, or "waste heat". This heat energy could be used in a variety of downstream process applications to provide an alternative to other energy equipment. The amount of the HRA was established as an emission rate of 40 g/GJ for natural gas and 60 g/GJ for liquid fuel, and would add 5-10 ppmv to the emission target of a typical cogeneration facility. The value of the HRA represents currently proposed NOx emission targets for industrial boilers in Initiative N306 (the alternative heat source). The rate is lower than that of the Power Output Allowance, because electrical or shaft power is a more valuable product than heat energy. Therefore a plant producing a larger proportion of power, versus heat extraction, from its fuel would be provided with a slightly higher NOx emission target. Many cogeneration plants will have steam readily available and may not need the higher allowance to operate. However, the control of NOx down to 45 ppmv instead of 40 ppmv would reduce the degree of required steam injection, thereby increasing overall efficiency and reducing associated emissions of carbon monoxide. The method to be applied in calculating the amount of useful heat energy for the HRA leaves some flexibility, in that difficult to measure downstream process losses can be ignored. The use of additional fuel in auxiliary duct burners in the heat recovery system will have to be taken account in assessing overall plant thermal efficiency. There is some evidence that duct-firing of additional fuel will create some of its own NOx' but may also actually destroy some of the NOx in the turbine exhaust. |
