Investigation of Pressurized Entrained-Flow Kraft Black Liquor Gasification in an Industrially Relevant Environment

Abstract

The University of Utah's project 'Investigation of Pressurized Entrained-Flow Kraft Black Liquor Gasification in an Industrially Relevant Environment' (U.S. DOE Cooperative Agreement DE-FC26-04NT42261) was a response to U.S. DOE/NETL solicitation DE-PS36-04GO94002, 'Biomass Research and Development Initiative' Topical Area 4-Kraft Black Liquor Gasification. The project began September 30, 2004. The objective of the project was to improve the understanding of black liquor conversion in high pressure, high temperature reactors that gasify liquor through partial oxidation with either air or oxygen. The physical and chemical characteristics of both the gas and condensed phase were to be studied over the entire range of liquor conversion, and the rates and mechanisms of processes responsible for converting the liquor to its final smelt and syngas products were to be investigated. This would be accomplished by combining fundamental, lab-scale experiments with measurements taken using a new semi-pilot scale pressurized entrained-flow gasifier. As a result of insufficient availability of funds and changes in priority within the Office of Biomass Programs of the U.S. Department of Energy, the research program was terminated in its second year. In total, only half of the budgeted funding was made available for the program, and most of this was used during the first year for construction of the experimental systems to be used in the program. This had a severe impact on the program. As a consequence, most of the planned research was unable to be performed. Only studies that relied on computational modeling or existing experimental facilities started early enough to deliver useful results by the time to program was terminated Over the course of the program, small scale (approx. 1 ton/day) entrained-flow gasifier was designed and installed at the University of Utah's off-campus Industrial Combustion and Gasification Research Facility. The system is designed to operate at pressures as high as 32 atmospheres, and at temperatures as high as 1500 C (2730 F). Total black liquor processing capacity under pressurized, oxygen-blown conditions should be in excess of 1 ton black liquor solids per day. Many sampling ports along the conversion section of the system will allow detailed analysis of the environment in the gasifier under industrially representative conditions. Construction was mostly completed before the program was terminated, but resources were insufficient to operate the system. A system for characterizing black liquor sprays in hot environments was designed and constructed. Silhouettes of black liquor sprays formed by injection of black liquor through a twin fluid (liquor and atomizing air) nozzle were videoed with a high-speed camera, and the resulting images were analyzed to identify overall characteristics of the spray and droplet formation mechanisms. The efficiency of liquor atomization was better when the liquor was injected through the center channel of the nozzle, with atomizing air being introduced in the annulus around the center channel, than when the liquor and air feed channels were reversed. Atomizing efficiency and spray angle increased with atomizing air pressure up to a point, beyond which additional atomizing air pressure had little effect. Analysis of the spray patterns indicates that two classifications of droplets are present, a finely dispersed 'mist' of very small droplets and much larger ligaments of liquor that form at the injector tip and form one or more relatively large droplets. This ligament and subsequent large droplet formation suggests that it will be challenging to obtain a narrow distribution of droplet sizes when using an injector of this design. A model for simulating liquor spray and droplet formation was developed by Simulent, Inc. of Toronto. The model was able to predict performance when spraying water that closely matched the vendor specifications. Simulation of liquor spray indicates that droplets on the order 200-300 microns can be expected, and that higher liquor flow will result in better distribution of liquor in the reactor.