Abstract
Optimisation of the Sasol-Lurgi gasification process was carried out by utilising the method of Factorial Experimental Design on the process variables of interest from a specifically equipped full-scale test gasifier. The process variables that govern gasification are not always fully controllable during normal operation. This paper discusses the application of statistical robustness studies as a method for determining the most efficient combination of process variables that might be hard-to-control during normal operation. Response surface models were developed in the process variables for each of the performance variables. It will be shown how statistical robustness studies provided the optimal conditions for sustainable gasifier operability and throughput. In particular, the optimum operability region is significantly expanded towards higher oxygen loads by changing and controlling the particle size distribution of the coal.
Highlights
The Secunda and Sasolburg plants in South Africa gasify approximately 30 million tons of bituminous coal per year to synthesis gas with an H2/CO ratio of approximately 1.8, which is converted to fuels and chemicals via the Fischer-Tropsch process
For the purpose of robustness studies, stone content was incorporated into the model as a linear effect
It was shown that pure gas yield production is maximised at low oxygen loads and maximum medium fraction of the particle size distribution (PSD) for unwashed coal [1]
Summary
The Secunda and Sasolburg plants in South Africa gasify approximately 30 million tons of bituminous coal per year to synthesis gas with an H2/CO ratio of approximately 1.8, which is converted to fuels and chemicals via the Fischer-Tropsch process. A total of 97 Sasol-Lurgi fixed bed dry bottom gasifiers, 17 at Sasolburg and 80 at Secunda, have a combined production of approximately 5.1 × 106 m3n/h dry raw gas, which is equivalent to approximately 3.6 × 106 m3n/h pure synthesis gas. In 1998 Sasol decided to isolate one Sasol-Lurgi MK IV gasifier at the Secunda site as a test gasifier. This gasifier was equipped with additional instrumentation, which included a more sophisticated raw gas measurement and a dedicated coal feeding system. The purpose of the tests was to further optimize product yields and to increase
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