Abstract
This paper quantifies the exergy losses of coal-based series polygeneration systems and evaluates the potential efficiency improvements that can be realized by applying advanced technologies for gasification, methanol synthesis, and combined cycle power generation. Exergy analysis identified exergy losses and their associated causes from chemical and physical processes. A new indicator was defined to evaluate the potential gain from minimizing exergy losses caused by physical processes—the degree of perfection of the system’s thermodynamic performance. The influences of a variety of advanced technical solutions on exergy improvement were analyzed and compared. It was found that the overall exergy loss of a series polygeneration system can be reduced significantly, from 57.4% to 48.9%, by applying all the advanced technologies selected. For gasification, four advanced technologies were evaluated, and the largest reduction in exergy loss (about 2.5 percentage points) was contributed by hot gas cleaning, followed by ion transport membrane technology (1.5 percentage points), slurry pre-heating (0.91 percentage points), and syngas heat recovery (0.6 percentage points). For methanol synthesis, partial shift technology reduced the overall exergy loss by about 1.4 percentage points. For power generation, using a G-class gas turbine decreased the overall exergy loss by about 1.6 percentage points.
Highlights
Coal-based polygeneration, which integrates chemical production and power generation, is a promising strategy for clean coal utilization [1,2]
The results are presented in the following sequence: (1) base case, (2) effect of technical solutions for the gasification block, (3) effect of designs for the methanol synthesis, (4) effect of gas turbine choices, and (5) the calculated potential efficiency improvement in the polygeneration system
The irreversible exergy losses caused by chemical reactions account for about 21% of the total exergy input, while the irreversible losses caused by physical processes account for 36%
Summary
Coal-based polygeneration, which integrates chemical production and power generation, is a promising strategy for clean coal utilization [1,2]. Today’s coal-based polygeneration systems can potentially be significantly improved by systematic optimization [3,4] and by applying advanced technical approaches [5,6,7]. Applying advanced technical refinements to each of these components can potentially improve the energy efficiency of the entire system, as summarized below. Recovering the sensible heat of syngas from the gasifier can reduce energy loss. Coal-water-slurry pre-heating technology offers another opportunity to boost energy efficiency during gasification [11], and ion transport membrane technology for air separation can significantly reduce the energy consumption for oxygen production [12,13,14]
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