|The Chinchilla Demonstration Facility combines UCG and GTL technologies Click to enlarge.
During the first half of 2009, the Linc Energy Limited Underground Coal Gasification (UCG) to Liquids demonstration plant at Chinchilla (earlier post) ran four major production campaigns each of which has seen further improvements in plant performance, according to the company. The May campaign has been the most successful operation to date, producing high-quality synthetic hydrocarbon products over the entire operating period. The demonstration plant has now operated over extended periods with the anticipated levels of reliability.
The first liquids were produced in October 2008, with improvements in operations over the past few months. Linc Energy says it can now use this abundant and relatively cheap gas to make synthetic liquid hydrocarbons (with a focus on diesel).
|“My aim was to prove that we could take UCG gas and turn it into liquids and we’ve done that. The next goal is to refine and capture this knowledge and design and build a 20,000 barrel per day commercial GTL facility and that goal is progressing according to plan.”
—Peter Bond, Linc Energy CEO
Underground Coal Gasification (UCG) is a process through which coal is converted in-situ (i.e., underground, in the coal seam) to a syngas that then is used as a fuel for power generation or as a chemical feedstock—e.g., to feed into a Fischer-Tropsch process for the generation of synthetic diesel. The UCG syngas, which undergoes sulfur removal and additional conditioning at the surface, is similar to syngas obtained from conventional surface coal gasification systems, but production is achieved at a much lower cost.
The US Department of Energy’s Lawrence Livermore National Laboratory points out that UCG offers the following benefits in addition to lower cost:
- Eliminates conventional coal mining, reducing operating costs, surface damage, eliminating mining safety problems.
- Accesses otherwise un-mineable coals (deep or thin seams), increasing exploitable reserves.
- Leaves gasification residuals underground.
- Eliminates costs, facilities, and environmental issues associated with transport/storage of mined coal or coal gasification residuals (e.g., ash).
- Reduces overall greenhouse gas emissions and has advantages for geologic carbon storage.
However, the lab notes, there are also some downsides:
- UCG has produced significant groundwater contamination and ground subsidence in some previous operations.
- The increase in exploitable coal possible with UCG may be less when site selection is constrained by geologic and hydrologic criteria to protect the environment.
- UCG is a non-steady state process—operations cannot be controlled to the same extent as surface gasification. Process variables vary as burn progresses and can only be estimated; flow rate and composition (heating value) of product gas will vary over time.
The Chinchilla GTL facility demonstrated that it can effectively clean UCG synthesis gas to the high levels of purity required for FT synthesis. The quality parameters include sulfur concentrations that are consistently below 50 parts per billion. Gas quality is validated by reliable on-line sulfur and oxygen analysis, the latter confirming effective control over residual oxygen levels down to parts per million.
The ability to produce clean UCG gas for the FT reaction also means that the UCG gas can be used in a number of other commercial applications requiring quality clean gas, such as chemical and fertilizer production.
The technical achievement with the synthesis gas cleaning has been matched with ongoing improvements in FT synthesis operations. The FT catalyst reduction process has been enhanced with resulting improvements over successive production campaigns in catalyst activity and CO and H2 conversion. This has resulted in increases in production rates in the GTL plant.
Laboratory scale FT reactors in the research laboratory at Chinchilla have confirmed over prolonged periods that H2 and CO conversions above expectations can be achieved. The UCG synthesis gas is drawn directly from the pipes of Linc Energy’s GTL operating plant at the inlet to the GTL plant reactor, giving Linc Energy the ability to run the Laboratory’s reactors on real time with identical gas that is being fed to the main reaction. This has provided Linc Energy with an ability to forecast and test various areas of performance that is beyond the capacity of most other operations.
The next stage of improvement work will again focus on increasing catalyst activity in the demonstration plant thereby increasing CO and H2 conversion and subsequently increasing production rates. The increases planned in CO and H2 conversion will result from further improvements in the catalyst reduction process and in reactor temperature management. The improvement in the actual catalyst utilized in the reactor will only add to the potential increase in production rates.
Linc is working to further improve the plant catalyst reduction system. A program of FT catalyst improvements and performance tests at laboratory scale (both in-house and external) is also being expanded with the results from this work being used as a key input to conceptual engineering.