Gas separation: processes – Liquid contacting – And deflection
Reexamination Certificate
2001-07-20
2003-03-11
Hopkins, Robert A. (Department: 1724)
Gas separation: processes
Liquid contacting
And deflection
C095S219000, C095S228000, C095S229000, C055S315200, C055S438000, C096S188000, C096S355000, C096S359000, C096S366000
Reexamination Certificate
active
06530978
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improvement in a process for removing particulate and aerosol droplets from a stream of gases. More specifically, the present invention relates to a more effective system for removing entrained particles and droplets of tar from a gas stream originating from a source such as a biomass gasifier so that the resulting cleaned gas stream is suitable fuel for operating an internal combustion device, such as an engine or turbine, which may be coupled to an electrical generator or can be utilized as a synthetic gas for subsequent processing. For the purposes of simplicity, an internal combustion device is discussed herein.
2. Description of the Related Art
Developing countries need decentralized sources of power, i.e. power systems for each remote community. In developing countries, where natural gas, petroleum products, or coal are not readily available to remote communities and hydropower is not possible, communities often have some local form of biomass that could serve as an energy source if that biomass could be converted to electrical power. Locally available forms of biomass might include rice straw or rice hulls, sugar cane bagasse, poultry litter, refuse, paper plant pulp sludge, switchgrass, waste resulting from extraction of olive oil from olives, peanut shells, sawdust or wood chips, wood bark, municipal solid waste, coconut shells, corn cobs, cotton stover, etc.
Industrialized nations have a heightened awareness of the environmentally deleterious effects of the production of “greenhouse gases” including carbon dioxide produced by the combustion of fossil fuels. Many nations have agreed to aggressively reduce their production of these “greenhouse gases” by encouraging the use of alternate, renewable energy such as biomass. A concurrence of nations was reached during the summit conference on the environment that was held in Kyoto, Japan several years ago.
Technology is currently available for converting biomass materials, by heating the biomass materials under starved oxygen conditions, to a gas stream that has sufficient heating value to operate an internal combustion device, i.e. in the range of 125 to 250 BTUs per standard cubic foot, depending on the biomass materials being processed. The resulting gas stream contains nitrogen, carbon dioxide, trace amounts of carry-over ash and tar, and calorific constituents of carbon monoxide, hydrogen, and some alkanes and alkenes. Gasification is recognized worldwide as an innovative method of converting biomass into energy.
However, one of the problems that has been experienced with converting biomass to energy is that the gas stream that is produced by gasification units is contaminated with particulate matter and with aerosol droplets of tar that can foul an internal combustion device unless they are efficiently removed from the gas stream prior to introducing the gas stream into the device. Currently there is not an economical method for effectively removing the entrained particulate matter and the aerosol droplets of tar from these types of gas streams. The reason that the particulate matter and aerosol droplets of tar can not be easily be removed from the gas stream is that a large portion of the particles and droplets are micron to sub-micron in size and are not effectively removed by traditional gas scrubbing processes.
The invention addresses this problem by first passing the gas that is generated by the gasifier through a high temperature cyclone separator to remove most of the carry over ash from the gasifier to prevent fouling of the downstream equipment. Then the gas that exits the cyclone separator is passed through an indirect gas cooler, a direct contact spray scrubber chamber, then followed by one or more enhanced vortex chambers. To achieve the desired cleanliness in the resulting gas stream, it may be necessary to employ two or more vortex chambers in series. When the gas exits the vortex chambers, it passes through an inducted draft fan, then finally through a heat exchanger where the gas is cooled to condense additional impurities and then a demister or mist eliminator where those impurities are extracted from the gas.
The high temperature cyclone separator operates at approximately 1,000 degrees Fahrenheit, thus removing the entrained fly ash without cooling appreciably. The cyclone separator is a conventional type of cyclone separator designed for high temperature operation. The cyclone separator removes approximately 90% of the ash that is carried over in the gas from the gasifier. Removal of this ash prevents fouling of the downstream equipment, particularly the indirect gas cooler located immediately downstream of the cyclone separator. Also, removal of the ash reduces the loading on the direct contact spray scrubber located downstream of the indirect gas cooler. Thus, the addition of a high temperature cyclone separator between the gasifier and the indirect gas cooler allows the system to operate for longer periods of time without being brought down for cleaning and allows the system to do a better job of cleaning the gas.
The indirect gas cooler is a shell and tube heat exchanger that cools the gas stream from the gasifier by indirect heat exchange with a cooling medium such as air or water. The direct contact spray scrubber employs a liquid hydrocarbon, such as used motor oil, to scrub out the particulate matter and some of the organic aerosols that are entrained in the gas stream as the gas stream passes through the direct contact spray scrubber.
Once the gas exits the direct contact spray scrubber, it enters the enhanced vortex or vortices. Each enhanced vortex chamber employs a high-speed fan to propel the remaining entrained droplets of tar against the inside surface of the vortex chamber along with additional oil. When the droplets of tar hit the oil coated inside surface of each vortex chamber, the droplets coalesce on the surface. The tar and oil mixture then gravity flows out of each vortex chamber, thereby removing the tar from the gas stream. The gas stream, having thus been cleaned of its particulate and aerosol impurities, then enters a low-pressure surge tank. If the gasifier is operating at a pressure less than atmospheric pressure, an induced draft fan may be employed to convey the gas through the system.
When the gas exits the vortex chambers, it passes through a heat exchanger that cools the gas to less than 120 degrees Fahrenheit, thus condensing additional impurities and water. Finally, the gas passes through a demister where the condensed impurities and water are extracted from the gas.
From here, the gas stream can be sent directly to the internal combustion device for mixing with combustion air so that it can be burned in such internal combustion device, such as an engine or turbine, which may be coupled to an electrical generator or can be utilized as a synthetic gas for subsequent processing.
SUMMARY OF THE INVENTION
The present invention is an improvement in a method for removing particulate matter and aerosols from a gas stream generated by a biomass gasification unit. The invention consists of first removing the excess ash by passing the gas through a high temperature cyclone separator, then cooling the gas stream, oil scrubbing it to remove particulate matter and some tars and to further reduce the temperature of the gas stream, passing the gas stream through one or more vortex chambers to remove additional tars, and finally cooling the gas to condense out more impurities and water and removing the condensate with a demister.
The high temperature cyclone separator operates at approximately 1,000 degrees Fahrenheit, thus removing the entrained fly ash without cooling the gas appreciably. The cyclone separator is a conventional cyclone separator designed for high temperature operation. The cyclone separator removes approximately 90% of the ash that is carried over in the gas from the gasifier. Removal of this ash prevents fouling of the indirect gas cooler located immediately downstream
McQuigg Kevin
Scott William Norman
Energy Process Technologies, Inc
Hopkins Robert A.
McKay Molly D.
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