- مبلغ: ۸۶,۰۰۰ تومان
- مبلغ: ۹۱,۰۰۰ تومان
Biomass torrefaction is a pre-treatment technology with high potential to convert biomass into a valuable commodity. The heat integration of torrefaction and combined heat and power (CHP) plant was investigated in previous work (Sermyagina et al., 2015). The aim of the present study is to assess possible economic benefits from integration. Three most promising integration concepts from the previous work were studied in terms of seasonal operational changes of district heating demand and varying ambient conditions. The performance of two integration concepts were evaluated together with stand-alone and co-located plants. The integration leads to a higher utilization of the CHP boiler capacity during part-load operation, possible increase of the operation time and growth of electricity generation as a result. The total efficiencies of the integrated cases (around 72% in higher heating value terms) are slightly higher than the stand-alone CHP plant (69%) or the co-located option (71%). The integration requires 40% more capital investments than the stand-alone CHP. On the other hand, the total capital investments of the integration cases are 20% lower than in co-located plants, and a profitability evaluation shows that lower investment costs may make integration schemes advantageous over the non-integrated plants. Feedstock price and investment costs are the main economic drivers affecting the profitability of the integrated options. An integration case which uses back pressure steam to account for the torrefaction heat demand showed the highest profitability due to a longer annual operating time, resulting in a growth of electricity and DH production over the stand-alone CHP plant.
5. Summary and conclusions
This study has shown that the heat integration of a torrefaction process into a CHP cycle could be economically profitable over the co-located plants under certain circumstances. While the previous investigation revealed important benefits of the integration with CHP at reduced district heating load, the analysis of the integrated cases considering seasonal operational changes brings a more complete understanding of the annual operation for each scenario. The typical backpressure CHP plant that was analysed in the present work fulfils the district heating demand and, as a result, follows all the annual variations of the DH network (both qualitative and quantitative). The operational analysis of the current study takes into account all major changes that affect the plants performance in order to evaluate the potential of possible integration. Three scenarios to cover the heat requirements of a torrefaction unit (30.3 MWLHV production capacity) were initially evaluated: drum water (Case 1), live steam and low pressure steam (Case 5) and only live steam (Case 6). The analysis showed that integration options using live steam to cover the torrefaction demand have significant benefits. Within the frames of the considered capacity levels and the limitations for the plant operation, the integrated scenario of Case 1 cannot be operated during full-load periods. Reducing the capacity of the torrefaction unit may result into certain improvements, but for purpose of keeping the cases comparable, only Cases 5 and 6 were considered in the current work.