Patent Application
20130008772
The invention provides for methods for using biomass to produce syngas or other chemical compounds in an efficient and environmentally friendly manner. The biomass is first converted into a liquid which is fed to a gasifier by itself or with a solid carbon-containing component which will convert the liquid into the syngas which can be recovered or further processed into additional chemical compounds.
With the desire to minimize dependence on coal, oil and gas, and to reduce the emission of carbon dioxide has arisen the consideration of biomasses for conversion into oil-based products. Biomass is typically wood, straw, plant deposits, woodchips, grasses and byproducts of farming and furniture manufacturing operations and other organic compounds. It is proving desirable to convert these biomass sources into oil-based products such as petrol, diesel, chemicals and plastics through the intermediate step of forming syngas (hydrogen and carbon monoxide).
A significant number of industrial and agricultural processes generate biomass, waste and by-products that contain polymeric sugars such as starch, cellulose and hemicellulose. The conversion of these biomasses into materials of higher value is of great interest to industry today. The use of biomass as a sole feedstock has certain disadvantages though. For example, biomass must be put into bales and loaded onto skids where it will be moved by truck or rail lines. These bales are heavy and are consequently expensive to move. Alternatively, a liquefied version of biomass such as biooil has a greater amount of stored energy than biomass and can be stored and transported in drums or tanks which are easier and more economical to transport than traditional methods of moving biomass.
Biomasses such as wood, straw and plant deposits can be converted into oil-based products such as petrol, diesel, chemicals and plastics through the formation of syngas by use of a gasifier. Syngas which is primarily carbon monoxide and hydrogen also contains some impurities. Gasification is a well-known technology where hydrocarbon bonds are broken down to produce syngas, under the addition of oxygen and stream, preferably under high pressures and temperatures. The amount of air or oxygen inside the gasifier is controlled so that the hydrocarbons do not combust into carbon dioxide but only oxidizes partially.
One obstacle to obtain the full benefit from gasification of biomass compared to for example coal is how to pre-treat the biomass in a way that makes it suitable to be economically gasified. Syngas production from coal gasification is a long standing commercially available technology. Coal is relatively easy to grind and feed into a pressurized gasifier; biomass in general is often difficult to grind and be fed into a pressurized gasifier. This is partially due to biomass being inhomogeneous compared to coal and is difficult to grind down to a relatively homogeneous particle size required for entrained flow gasification where the residence time is very short. Furthermore, it is also difficult to pressurize a solid material with very uneven and larger particles size.
Traditionally, biomass to be fed into a gasifier has been pretreated using such methods as direct pulverization, combustion and pulverization, production of charred sludge through flash pyrolysis or production of gaseous fuels through low temperature fluid-bed gasification. Previous methods include pneumatically or by means of screw conveyors injecting biomass as a fine solid powder into a gasification reactor. This process requires grinding and drying steps. Since gasifiers are typically large units, there needs to be substantial on site preparation of the biomass to accommodate this option. All these processes add to the cost of using biomass but have difficulties in that specialized equipment now needs to accompany the gasification process which might not always be readily accomplished.
The mixture of the liquefied biomass and solid carbon-containing component is easier to feed to a gasifier than pure biomass. The combination of the liquefied biomass and solid carbon-containing component contains more energy than the liquefied biomass by itself. The use of the liquefied biomass and solid carbon-containing component allows for high pressure operations at the gasifier and results in downstream savings as additional compression equipment will not be required to raise the pressure of the gasified product for further downstream processing or feeding to designated storage units.
The present inventors have discovered a new method whereby biomass is introduced into a gasifier either by itself or with a solid carbon-containing component. The biomass is first converted into a liquid (pyrolysis liquid or biooil) which can then be added to the gasifier as a pumpable slurry allowing for the conversion of the biomass into syngas without the necessity of grinding, pulverization or other mechanical treatments.
The invention provides for a method of gasifying biomass comprising the steps of converting the biomass into a liquid, adding a solid carbon-containing component and feeding the combination of liquid biomass and solid carbon-containing component into a gasifier.
The invention further provides for a method of gasifying biomass comprising the steps of converting the biomass into a liquid and feeding the liquid into a gasifier.
Alternatively the invention provides for a method for producing syngas comprising the steps of converting biomass into a liquid, gasifying the liquid and recovering syngas.
The gasification process can be used to produce other syngas based chemicals through for example the Fischer-Tropsch reaction or integrated gasification combined cycle (IGCC) or the gasification products can be used for power generation purposes. These chemicals can include hydrogen, carbon monoxide, hydrogen/carbon monoxide mixtures, methanol, ammonia, and synthetic natural gas (SNG).
The biomass for purposes of the invention comprises wood, straw, plant deposits, woodchips, grasses forestry waste, municipal solid waste, waste water sludge, manure, waste fats and byproducts of farming, furniture manufacturing operations or other industrial process where organic plant stuff is a by-product or waste. The biomass is first fed to a pyrolysis unit where it is subjected to high temperatures for short durations of time. These rapid pyrolysis reactions are typically performed at temperatures greater than 400° C. and near atmospheric pressures in a relatively oxygen-free atmosphere in the presence or absence of a catalyst and also in the presence or absence of hydrogen.
The resulting reactions will form a mixture of gas, char and a liquid (biooil or pyrolysis oil) where the liquid portion is about 70% of the biomass converted.
In a different embodiment, the liquid portion of the converted biomass can be combined with one or more fuel stocks such as coal, biomass, biocoke, coke or other solid carbon-containing component for purposes of the invention which has greater carbon (fuel) content than the converted biomass liquid. The solid carbon-containing component can be added in any amount to the mass of the biomass liquid as long as the appropriate viscosity is maintained such that the resulting slurry can be readily fed to the gasifier.
As an optional step, the liquid can be purified by processes such as vacuum distillation or phase separation prior to it being fed to the gasifier.
The FIGURE is a schematic of the gasification process of the invention.
The FIGURE is a schematic of the operation of the invention. Biomass which is selected from the group consisting of wood, straw, plant deposits, woodchips, grasses forestry waste, municipal solid waste, waste water sludge, manure, waste fats and byproducts of farming, furniture manufacturing operations or other industrial process where organic plant stuff is a by-product or waste is fed through line 1 to a pyrolysis unit A. The biomass may be treated beforehand to a shredder/crusher (not shown) in order to allow for easier feeding into the pyrolysis unit A. In the pyrolysis unit A, fast or rapid pyrolytic reactions are performed on the biomass at temperatures greater than 400° C. and at near atmospheric pressures in an atmosphere that is low in oxygen content. A catalyst may or may not be presence in the pyrolysis unit A and hydrogen may or may not be present in the pyrolysis unit A either.
The by-products of the pyrolytic reaction will exit the pyrolysis unit as char through line 2 and as a gas through line 3. The pyrolysis liquid which is about 70% of the mass of the biomass will exit the pyrolysis unit A through line 4 where it will be fed to an optional purification unit B such as vacuum distillation, phase separation operations or other known separation processes.
The purified pyrolysis liquid will exit the purification unit B through line 5 and enter the gasifier C. Additional carbon fuel stock compounds such as coal, biomass, biocoke, coke (“solid carbon-containing component”) may be added to the gasifier C through line 6 which connects to line 5 prior to entering the gasifier C. The only caveat with regards to the addition of the solid carbon-containing component is that the pyrolysis liquid remains viscous enough to be pumpable into the gasifier C.
In the gasifier C, the pyrolysis liquid will be reacted at high temperature in the presence of a controlled amount of oxygen and/or steam. The resulting gas mixture is syngas or a mixture of carbon monoxide and hydrogen. The syngas can be removed from the gasifier C through line 7. Reaction by-products such as char can be removed through line 8 and in some instances can be recycled to line 6 for reentry into the gasifier C.
While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of the invention will be obvious to those skilled in the art. The appended claims in this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the invention.
