23-02-2012, 01:16 PM
Well, if in the backpressure mode you will get X tonnes (or kt, or Mt, whatever unit you choose) hot water or steam per one PJ of electricity produced, you should set your NCAP_CHPR value to X. Of course, you should then model the demand of the heat also in the same unit.
You can model the plant in terms of BP-mode electrical efficiency by setting NCAP_CEH to zero.
So, if your BP mode electrical efficiency is 35%, you should set ACT_EFF=0.35 and NCAP_CEH=0.
I added the COM_LIM(FX) parameter only because you had not modeled any heat demand, just for making the heat consumption visible in the results. Normally, you should model the heat demand in order to have some value for the heat as well. If you have no heat demand, the heat has basically no value, and Cogeneration would hardly ever become economical. But when you have the demand, there should be no need to make the commodity balance fixed by using COM_LIM(FX).
So, I would certainly not recommend using the COM_LIM(FX) for every commodity. It is mostly only useful in cases where the commodity has no positive value as such (e.g. waste), but must be further processed or treated before it can be either disposed of, or converted to a product that has a positive value. In such cases the open commodity balance equation (≥) would make it possible to dump the waste without costs to anyone's backyard, which should thus better be prevented by setting the COM_LIM(FX) parameter, or bounding the VAR_COMNET variable to zero.
Concerning dummy import processes, they can indeed be useful for avoiding infeasiblities in the model, but you should not set the costs overly high, because that is likely to cause numerical problems.