Interated Design For Grading Lignite Pyrolysis Oil Production System And CO₂Emission Control

The huge energy demand for the future sustainable development and theenergy resource structure of our country strengthen the importance and urgencyof rational use of coal. And in the new era, new requirements and constraints areput on this process, such as element effective utilization and CO2emission.In view of energy resource, lignite is a low-rank one that has not beeneffectively utilized. It is not only a waste of resource, but also causes seriouspollution if the lignite is not put into a proper process. As for the energyproducts, gasoline and diesel known as the driving power of some machines,vehicles and planes are the guarantee in the field of industry and transportation.With the economy level going up, the future demands will also keep rising for arelatively long time. In terms of element utilization, carbon will prolong itslifetime cycle if the high carbon contained resource can be converted into carbonbased materials as much as possible. Furthermore, with the development ofeconomy and more attention being paid to environment protection, the appealingfor CO2emission reduction also get stronger.This paper summarized the features of coal utilization process which is focused on the carbon as the key element. And it was realized that thedevelopment of polygeneration systems was really an important choice for coalchemical industry. And according to these two points, researches are conductedon deep processing of lignite. Supported by natural science foundation of China“integration optimization theory basic research on grading lignite pyrolysispolygeneration system” and “theoretical and technical basic of coal-basedpolygeneration with CO2emission reduction”, in this paper, a co-generationsystem of lignite pyrolysis-oil production-power generation is set up, which isbased on the former work of lignite fast pyrolysis by solid heat carriers. Andbased on the new system, attention is also paid in the effects of methanereforming on the lignite to oil system, in which the feeding methane is obtainedfrom the system itself. By turning to chemical process simulating softwareAspen Plus, energy conversion, material balance, economy analysis and CO2emission calculations are conducted for this lignite based pyrolysis originateddeep processing system as the feedstock characteristics, key units’ variables,prices of feedstock and products change from case to case.The research results imply that the coupling of tar hydrogenation andFischer-Tropsch synthesis could add to the oil output and share some equipment,which save fixed investment. On the other hand, by coupling, the unit oilconsumption and CO2emission also decrease making the lignite based oilsystem competitive to other high rank coal based oil production system inevaluation indexes. From the analysis of system key variables, some results and conclusions are obtained as follow:1) It was found that under a fixed pyrolysis scale, the moisture of lignitemainly affects the downstream scale. Too small a pyrolysis scale is detrimentalto the economy performance. As for the whole production system, the scalematching among the pyrolysis unit, gasification unit and oil production unit isone of the key elements.2) The gasifier will make differences on H2generatingload and the energy efficiency.3) The electricity power plant will add to thefixed investment and pull the energy efficiency down, but since the coal to oilsystem is a heavy power consuming one, the extra power plant could actuallyenhance the economy performance.4) In the aspect of energy efficiency, theShell gasifier adopting process is better, and it could reach to41.8%or a little bitdeclines to38.9%if power plant is added. In the economy aspect, the internalrate of return is as high as15%under the best price case assumption, and thatcan be near18%for Texaco gasifier adopting processes.5) The unit oil emissionof CO2is7.5-9.5tonne. The main contributor of energy consuming and CO2generating is the pyrolysis unit. And by applying the reforming of internalmethane, it was unable to reduce the CO2emission, but could slightly increasethe oil output, and this is caused by its limited scale.