The Reemergence of Gasification for Energy and Fuels
The de facto standard for converting biomass to heat and electricity is combustion in a high-pressure boiler system. From a thermal perspective, this is the simplest and most reliable technology. Biomass is simply combusted and the heat is used to boil water to high pressure through a heat exchanger. The air and biomass inputs to the boiler are easy to control and provide a wide tolerance range for flow deviations. A little too much or too little air flow affects peak combustion temperature but does little to the overall thermal energy transferred to steam.
Environmental concerns and the desire to convert carbonaceous fuels to liquid fuels are refocusing research back to an old technology that was supplanted by boiler systems. Gasification was once used extensively to produce “town gas” from coal, to pipeline to homes and streetlamps for lighting and cooking in the 1800s. The technology was labor-intensive and dirty, but produced industrial quantities of tars and coke, around which whole industries revolved, converting these wastes into salable products. Electricity and natural gas, both cleaner and more economical, supplanted town gas in the 1900s.
The resurgence of gasification technology is focusing on producing high-value chemicals and fuels, in addition to cleaner and more efficient power plants utilizing both gas turbines and steam turbines. The fundamentals of gasification have not changed, however.
What has changed to make it a viable technology once again is advancements in economical gas-cleaning technologies. At the Energy & Environmental Research Center, industry is partnering with government to develop, test, and commercialize clean gasification technologies.
The EERC has designed and constructed a wide range of gasifier technologies, including fixed-bed, fluidized-bed, and entrained flow-gasifiers, to meet the needs of different segments of the energy industry. Innovative fixed-bed and fluidized-bed gasifiers have been used to test and develop systems that operate on wood, grasses, turkey litter and sewage pellets. Both fluidized and entrained-flow gasifiers have tested the viability of cogasifying biomass and coal for integrated gasification combined-cycle plants.
The know-how in utilizing biomass fuels in gasifiers is constantly being improved. In addition, different system configurations and operating conditions are constantly being applied to employ alternative downstream gas cleanup and conversion technologies, such as ceramic filters, gas membranes, fuel cells, microturbines, ammonia catalyst and Fischer–Tropsch reactors.
Each segment of the energy industry has a unique set of economic, environmental and operating constraints that dictate the type of gasifier used and system configuration.
Biomass, in particular, poses challenging constraints that differentiate it from the more economical and developed coal gasification systems. The distributed nature of biomass and variable chemical and physical compositions of biomass require a much higher degree of outside-the-box thinking to develop not just the technology, but also a matching business model that gives value to potential customers.
Systems are currently being developed and tested to utilize internal combustion engines, high-temperature fuel cells, and microturbines to produce power and heat from biomass. Since biomass is highly distributed by nature, the primary approach at the EERC is to develop sub-megawatt-sized systems and business models that can be economically employed at the source of biomass production, eliminating the high costs of transporting the biomass to a centralized power station.
In the upcoming months, articles will be provided to Biomass Power & Thermal magazine summarizing some of the benefits and challenges of each of these systems tested at the EERC.
Author: Phil Hutton
Research Manager, Energy & Environmental Research Center