M.Sc Thesis

M.Sc StudentShvarzfarb Anna
SubjectDeveloping Two-Chamber Biomass Gasifier
DepartmentDepartment of Energy
Supervisor PROFESSOR EMERITUS Yehoshua Dayan
Full Thesis textFull thesis text - English Version


The research proposes developing, proving the concept and demonstrating a two-chamber reactor for gasification (2CG) of biomass and low-grade fossil fuels such as oil shale and bitumen. The composition of the produced syngas will determine its optimal utilization - conversion into liquid transportation fuels, petrochemical feedstock, or fuel for gas turbines and fuel-cell systems. In most gasification methods, a small part of the feed is burnt to supply the necessary heat for the endothermic gasification reactions. Classical processes were based on cryogenic air separation to extract oxygen for the burning while avoiding syngas dilution by nitrogen. Most of the recent development use solid particle circulation to transfer heat between two reactors, slow fluidized bed gasifier and fast fluidized bed combustor. In the combustor residual feed, mixed with cooled solid particles from the gasifier, is burnt in air, heating up the particles, which are circulated back to the gasifier to supply the heat for the endothermic gasification reactions between the feed and steam. Similar to the other modern approaches the 2CG is also employing solid particle circulation to transfer the heat from the combustor to the gasifier. However, unlike the other approaches, the two rectangular cross-section reactors, are built as two adjacent chambers with common wall in one reactor. Moreover, the gasification occurs in a downwards moving packed bed regime, rather than fluidization. The residual unreacted organics, mixed with the cooled particles, enter from the bottom of the gasification chamber into the fast fluidized bed combustion chamber, and the reheated particles are spilled over, back onto the gasifier, through a cyclone, which blocks flue gases penetration. The two different flow regimes wrong gas penetration, while the rectangular configuration offers easy scale-up for future commercialization and significantly reduces heat losses. During the first research stage a cold pilot system was designed and built to determine optimal reactor structure, connections forms, separation equipment, circulation flows and to minimize the stagnant areas. Optimal flows parameters were found and air leakage from the combustion chamber to the gasification was quantified to contain less than 3.5% Nitrogen. Sawdust was selected as biomass feed for the high temperature testing, ensuring suitable composition and proper Low Heating Value for the expected syngas product. Based on the results obtained from the cold system the hot reactor was designed and built, mass and heat balances were calculated, and the start-up procedure developed. Hot testing started in a subsequent research.

Other parallel complementary efforts were also conducted in conjunction with this thesis. These included: Control system design for the process, searching for the best catalyst to boost the syngas H2/CO ratio at a lower temperature and developing a simplified model for the 2CG in order to facilitate future commercial designs.