Design and Economic Evaluation of a Coal-Based Polygeneration
Process To Coproduce Synthetic Natural Gas and Ammonia
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Abstract
The
steady-state design and economic evaluation of a polygeneration
(POLYGEN) process to coproduce synthetic natural gas (SNG) and ammonia
are studied in this work. POLYGEN has been a widely studied topic
recently, in which several products could be produced parallel at
the same time. One of the two products in this study, SNG, has a composition
and heat value very similar to those of typical natural gas, and can
be used as a replacement in industrial and home usages. Another product,
ammonia, is one of the most important inorganic chemicals in the world,
and could be used as the precursor of various kinds of chemicals,
as fertilizers, or as a cleaning agent. In the POLYGEN process, the
relative production rates for different chemicals could be adjusted
on the basis of different market demands, daily usages, and also changing
political strategies. In our previous study (Yu, B. Y.; Chien, I.
L. Design and Economical Evaluation of a Coal-to-Synthetic Natural
Gas Process. <i>Ind. Eng. Chem. Res.</i> <b>2015</b>, <i>54</i>, 2339β2352), we illustrated that the
SNG production price is lower than the liquefied natural gas importation
price in Taiwan. The SNG production price is 10.837 USD/GJ (USD =
U.S. dollars) in an SNG-only plant. With the POLYGEN process to coproduce
SNG and ammonia, the SNG production cost could become even lower.
If 20% of the syngas is used to produce ammonia, the SNG production
price will drop to 9.365 USD/GJ, and if 40% is used for ammonia production,
the SNG production price will drop further to 7.063 USD/GJ. Thus,
although the POLYGEN process leads to an increasing total capital
investment, it has positive influences from economic aspects. Besides,
the flexibility of shifting the production rate of SNG or ammonia
makes it possible to adapt to changes in the market demand