Gasifier, time response

Some work has already been done on the simulation of transient behavior of moving bed coal gasifiers. However, the analysis is not based on the use of a truly dynamic model but instead uses a steady state gasifier model plus a pseudo steady state approximation. For this type of approach, the time response of the gasifier to reactor input changes appears as a continuous sequence of new steady states. 

The upper curve was calculated by the method of characteristics program and it exhibits a true limit cycle or sustained oscillation response (19). The middle curve was calculated by the distance method of lines program. The response is attenuated and stretched out. The final long term oscillations had random unequal periods and they were out of phase with the MOC results. The lower curve was calculated by the time method of lines program. The initial part of the response is similar to the DMOL results but then the temperature incorrectly levels out to a steady state condition. Thus, it was evident that the distance and time method of lines techniques were not as accurate as the method of characteristics procedure for calculating the gasifier step responses and they were discarded. 

Step change dynamic response runs revealed that the distance and time method of lines techniques were not as accurate as the method of characteristics procedure for calculating gasifier transients. Therefore, these two techniques were discarded and the remaining calculations were all done using the method of characteristics. 

---