Energy Research Group, Chemical Engineering and Applied Chemistry Department, Aston University, Aston Triangle, Birmingham B4 7ET, UK
Abstract
Since the oil crisis of 1973 considerable interest has been shown in the production of liquid fuels from alternative sources. In particular, processes utilizing coal as the feedstock have received considerable interest. These processes can be divided into indirect liquefaction, direct liquefaction and pyrolysis. This paper describes the modelling of indirect coal liquefaction processes in order to perform a consistent technical and economic assessment of the production of liquid fuels from coal and lignite, using a variety of gasification and synthesis gas conversion technologies. The technologies are modelled on a ‘step model’ basis where a step is defined as a combination of individual unit operations which together perform a significant function on the process streams, such as a methanol synthesis step or gasification and a physical gas cleaning step. Sample results of the modelling are presented to illustrate the scope of the work. These cover a representative range of gasifiers, liquid synthesis processes and products from the large number of combinations of feeds (3 alternatives), gasifiers (10 alternatives), products (6 alternatives), other technical parameters (up to 20 variables) and economic or financial parameters (17 variables), as well as possible sensitivity studies. The results have been validated by major European companies in absolute as well as comparative terms. The main results show that methanol is the most attractive fuel relative to current market prices, followed by fuel alcohol (a mixture of alcohols produced by modified Fischer-Tropsch synthesis), diesel from the Shell middle distillate synthesis process, diesel from the Mobil methanol to olefins gasoline diesel process, gasoline from the same process and finally gasoline from the Mobil methanol to gasoline process. Some products are currently economic based on typical world coal prices. There was a variation in production costs of up to 100% for most products depending on the type of gasifier chosen and specific feedstock."
First of all, in 1991, British researchers knew enough about no fewer than "10 alternatives" for transforming coal into other, more malleable, forms to hold discourse on those alternatives.
And, they were kind enough to name several of those alternatives, which you should by now be familiar with, such as the venerable Fischer-Tropsch, Shell MDS, and Mobil (now ExxonMobil) MTG technologies. If you have followed our coal liquefaction posts thus far, the names, and general outlines, of those technologies should be familiar to you; and, a sense of what the reality of their largely-unacknowledged existence implies should by now have dawned.
Note that, in 1991, these British researchers were able to study multiple "processes ... to perform a consistent technical and economic assessment of the production of liquid fuels from coal ...using a variety of ... technologies."
Why, very nearly two decades later, do we, in the US, seem publicly unable to do the same? And, in those two decades of constantly-rising oil prices, could the "economic assessment" of coal-to-liquid conversion have done anything but grown more favorable?