Preparation And Gasification Of Coal/Bio-oil Slurries

Biomass is the only renewable and carbon neutral energy resource in nature, and its utilization would help the reduction of CO2 emission as an alternative fuel. Due to the wide distribution, low energy density and danger of spontaneous-ignition for long time storage, the concept of a regional flash-pyrolysis and a central gasification and synthesis is more suitable for biomass utilization, because this would minimize the transportation cost. The first step of this concept is flash-pyrolysis of biomass and its main products are pyrolysis liquids (or bio-oil), char and gas. The bio-oil is then sent to central plant for syngas production. Bio-oil exhibits high oxygen content, high water content, strong acidity and instability, and all this makes it difficult for direct utilization. One of the effective applications of bio-oil is to make slurries with coal for the preparation of coal/bio-oil slurry. With coal added into bio-oil, the suspensions have much higher calorific value than bio-oil, and the bio-oil in turn contributes much more heat to coal/bio-oil slurry than coal/water slurry with the same coal concentration. Thus coal/bio-oil slurry could also be considered as a partial green fuel. This research focuses on the process of coal/bio-oil utilization which involves the rheology, atomization and gasification of the slurry.Firstly the rheology of coal/bio-oil slurry was studied to select the proper slurry composition. The influence of coal rank, solid concentration, particle size distribution and temperature on apparent viscosity of slurries were investigated. Based on grey relational analysis, moisture and carboxyl groups in coal are determined as main factors affecting the apparent viscosity of coal/bio-oil slurries. Slurries prepared by bituminous coal and anthracite presents lower apparent viscosity. The maximum solid concentration can reach 45% for Shenmu bituminous coal.Atomization of slurry is the first step before feeding into gasifiers, it is also a key process in industry. Atomization performance of pilot-scale atomizers for feeding of coal/bio-oil slurry in an entrained flow gasifier was studied. Advanced techniques were applied to measure the size of slurry droplets with a high speed infrared camera followed by digitalization of a series pictures automatically. The effects of coal concentration in slurry, gas flow and slurry flow on average size of the droplets and velocity of the droplets were investigated. The profiles of droplet size and droplet velocity were also provided to determine the development of the spray. The selection of nozzle and operating conditions are applicable in the slurry-fed entrained flow reactor in Technicial University of Denmark.Gasification of coal/bio-oil slurry was carried out in an entrained flow reactor with the temperature range of 1200-1400℃, which provides a feasibility for coal/bio-oil slurry gasification in industry. Its gasification performance was compared with that of coal/water slurry. Results show that the carbon conversion of coal/bio-oil slurry reached 95% and it was much higher than coal/water slurry in experiments. Gasification of coal/bio-oil slurry and coal/water slurry based on industrial parameters were calculated using Aspen Plus, and the cold gas efficiency of coal/bio-oil slurry is 3% higher than that of coal/water slurry.The characterization of the solid products from coal/bio-oil slurry gasification was a supplementary to get a deeper understanding of this process. Results show that fly ash obtained from coal/bio-oil slurry gasification presents higher gasification reactivity than those from coal/water slurry. Fly ash collected in filter from coal/bio-oil slurry gasification has higher gasification reactivity than those collected in cyclone. AAEMs in bio-oil especially K plays an important roal in enhancing gasification reactivity.