A biorefinery is a plant that converts biomass into useful products such as fuels, chemicals and power. Three types of refineries are being used and developed:
- Sugar platform biorefineries, as exemplified by ethanol plants, are in widespread use, are based on the fermentation of sugars.
- Close coupled systems that primarily produce fuel that can be used to produce power or heat from either syngas or pyrolysis oil.
- Thermochemical refineries that are more analogous to petroleum refineries which can produce an array of products in addition to fuel and power.
The sugar platform refineries refineries are in common use, producing 3.41 billion gallons of ethanol, in the U.S., in 2004. These have been developed significantly since they were first used. In the 1980's they were rather simple facilities that fermented corn to produce ethanol. The process has developed rapidly and today they are highly integrated facilities that are much larger, use much less energy, less manpower and produce byproducts as well as ethanol; thus reducing the production costs significantly. However the cost of the feedstock, the largest single cost, has not gone down significantly and the quantity available will be limited by land availability at some time in the future if only corn is used as the feedstock. New pretreatment techniques are now starting to be used that permit recovering the sugar from the cellulose in the corn residues that were formally wasted, thus increasing the supply of feedstock greatly. In the next few years it is anticipated that the industry will be able to process any cellulosic material, such as grasses, willows, municipal solid waste and forest residues; increasing the availability of feedstock by orders of magnitude.
Close coupled pyrolysis systems are available commercially and are used to produce fuel for engines or gas turbines or to supply heat for boilers for either heating or generating electricity. These systems are relatively small, but fill a need for generating energy in relatively remote locations. These systems are more widely used in Europe where energy prices are higher than in the U.S. It is expected that they will be more widely used in the U.S. as more conventional energy prices escalate.
Thermochemical refineries, also known as Bio-Gas Fischer-Tropsch refineries (BG-FT), are still in the early developmental stage with only a few small commercial units in operation. They offer the advantage that almost any fuel or petroleum like product can be produced using this method. This is the only way that diesel fuel can be produced in large quantities using biomass as the feedstock supply. The supply of biodiesel will eventually be limited by available land unless a more efficient feedstock, such as algae, is able to be used. Their are some technical problems to be solved in the BG-FT process, but suppliers are finding some niche markets where these problems have been overcome.
The Renew consortium in Europe has 31 partners from 9 countries was formed to prove different concepts of fuel production from biomass. This paper "Presentation on 1 year progress of RENEW" describes the first years work of the consortium. They are assessing several biorefinery routes to several liquid fuels using five different biorefining routes, all using gassification and 3 using FT synthesis .
DOE has all but stopped funding thermochemical refineries while they sponsor research to solve the technical problems, largely related to cleaning up the syngas so that it will not degrade the performance of the FT unit, and have given other unrelated programs higher priority. This technology is the only one that gives us the capability to produce the wide variety of products that are now produced in a petroleum refinery. We should establish a policy that will demonstrate a medium scale BG-FT biorefinery at an earlier date than would, if ever, happen with our current policy. The DOE has a small Process Demonstration Unit (PDU) that they are using to solve the problems of cleaning up the syngas produced by biomass gasifiers, but this does not demonstrate the feasibility on a large scale.
The next year should be spent developing a design concept. Funds for this should be redirected from other projects.
- Europe has a vast knowledge in building biomass gasifiers, as we know as a member of IEA Task force 33. The U.S also has considerable know-how in the companies that have been doing biomass gasifier development and in the large companies with coal gasification experience.
- The plant should be designed around a feedstock that is known to produce small amounts of tars, like wood chips, when gasified. Then as technology is further developed by industry and in the PDU, the plant can be modified so that other feedstocks can be tested.
- Gas cleanup technologies are also known, though not as well developed. A gasifier that produces the cleanest syngas should be used. Pearsons has been able to use off the shelf gas clean up equipment in their plants.
- Fischer-Tropsch technology is well known and the technology could be procured from one of the four major suppliers.
- A rather simple refining step should be employed, with power recovery and byproduct recovery added at as time and technology are available.