The synthesis of many chemicals begins with a hydrocarbon source, frequently crude oil or natural gas. In situations of high price or limited availability of these resources, coal/petcoke (possibly supplemented by a wide variety of feedstocks such as refinery waste, biomass, and municipal waste) is a viable alternative. Producing chemicals from coal is a way to increase energy security and diversity, and as the Eastman Coal-to-Chemicals plant has shown, it can be done profitably and with good reliability. From a market standpoint, chemicals are growing in demand, especially in rapidly developing China. Environmentally, the syngas cleaning process can reduce emissions below regulated standards and is well-positioned if carbon dioxide capture becomes regulated. Steam produced by the gasification process can often be effectively integrated to meet a chemical plants needs, increasing efficiency. Chemicals production from coal is also well-suited to cogeneration with an IGCC power plant, because of the way each can respond to product demand, as explained in discussion of cogeneration.
Challenges in the area of chemicals production from coal are similar to the challenges that face other gasification applications, mainly cost (capital and operating/maintenance) and availability. For the production of some chemicals like methanol, ammonia, acetyls, etc., the economics of coal-to-chemicals are favorable—the Eastman Coal-to-Chemicals plant is profitable, for example—and so cost is not a barrier to project realization. The economics of gasification can continue to be improved, however. Increased availability, either through new materials or better maintenance methods, is also an area where research and development could lead to substantial improvements. These general gasification challenges are discussed in the linked discussion in Introduction to Gasification. Research and development ideas are also discussed below.
The Eastman Coal-to-Chemicals Plant in Kingsport, Tennessee, lists production rate, reliability, maintenance cost, and safety as primary importance to the facility's operation. Increasing process efficiency to produce more product over a period of time or per coal input helps defer high initial capital costs. Related to, and perhaps more important than, production rate is reliability. An outage can have drastic consequences on the economics of a plant, so availability is an important factor to consider during planning. Through a well-defined maintenance schedule, redundant units, and improvements to problem areas (identified through a consistent "run review" schedule), the Eastman plant has been able to demonstrate over 98% gasifier uptime since 1986. Eastman also found that having more frequent, planned maintenance—even though it increased turnaround time—has lowered the number of failures, increased production, and decreased overall maintenance costs. Similarly, by having plans and procedures in place, the plant has been able to establish an excellent safety record.
Problem areas identified by Eastman are similar to other gasifiers, mainly materials issues such as feed injector (burner) failure from corrosion and refractory wear. Eastman has found that routine maintenance and improvements from research and development have substantially reduced these problems.
R&D in Coal-based Chemicals Production
Many of the research and development avenues being undertaken for other gasification applications will also have beneficial results for chemicals synthesis from coal. For example, novel membrane-based air separation methods, show promise towards lowering the cost of pure oxygen supply for gasification. This would lower the energy and operation costs of the gasifier system and possibly the air separation unit's capital costs. Clean-up methods could allow for higher temperature or more efficient syngas clean-up, which would also reduce costs associated with heat loss and operation. Research into increasing gasifier availability, much of which has been done by Eastman specifically related to coal-to-chemicals, will increase the productive and profitable periods of gasifier operation while also reducing maintenance costs.
Some of Eastman's research and developments include:
Procedures for virtually seamless switching between gasifiers (cycling the spare) for maintenance