Molten Metal Gasification:
An emerging new design of gasifiers is the Molten Metal Gasifier. A number of different designs are in the early stages of development but the basic concept is that instead of using a formed gasifying chamber where the reactions occur in suspension, the feedstocks are gasified in a molten bath of metal. This allows for more complete processing of the feedstock and also allows for a greater variety of feedstocks to be efficiently processed in the same gasifier.
Remember that a typical gasifier is much like a hot air popcorn popper — it works well but if the material inserted into the reaction chamber isn’t of consistent size, mass, and moisture content, it degrades the efficiency of the gasifier. Because of these issues, current gasifiers require extensive pre-processing of the feedstock to obtain proper size and moisture as well as post-processing of the gases to remove impurities. The molten metal bath overcomes this through the enhanced heat retention of the metal and the more complete application of the heat from a liquid as opposed to flowing air.
Theoretically, the molten metal should also allow for some of the catalysis processes to take place within the gasifier instead of downstream. For example, in the Hydromax design, the hydrogen and CO are produced in separate distinct streams eliminating the need for post-process separation prior to catalyzing into synthetic fuels. When combined with reduced pre-processing, this should result in significantly lower capital costs compared to conventional gasifiers as well as lower operating costs over time.
The molten metal gasification process also allows for a greater variety of co-products to be produced on-site. All gasification methods allow for the co-production of various chemicals and gases but the molten metal process adds various metals, such as vanadium and nickel, to the mix. Most materials that originally existed in the ground, such as coal and petroleum coke, contain these metals which can then be extracted in the molten metal process, instead of being disposed of as slag. Also, molten metal reactors require the use of a fluxing material, such as lime or limestone. When combined with the silica ash that is generated through normal gasification, the slag produced and removed from the molten metal reactor can be used directly as cement or formed into bricks for construction materials.
FASTOX™ Technology and Other Iron & Steel Making Systems:
Sierra Energy in Davis, CA has proposed a new design of gasifiers that sort of combines the attributes of the fluidized bed gasifier with the higher heat retention of other gasifier designs. Called FASTOX™, this design is based on conventional blast furnaces used in the manufacturing of steel. FASTOX™ presents an interesting concept in that the infrastructure is adaptable to existing systems. Moreover, the FASTOX™ system offers the potential for massive scalability. Based on comparable existing blast furnaces, this design should be scalable to the processing as much as 25,000 tons of feedstock per day producing over 60,000 barrels of synthetic fuels from a single unit.
As has been demonstrated by the FASTOX™ prototypes, the basic systems involved in processing iron and steel and converting them into useful products are remarkably similar to the systems involved in gasification. FASTOX™ happens to be based on the blast furnace but plasma gasifiers are also quite similar to the electric arc furnaces used in most steel mini-mills and iron foundries. The only real fundamental difference is that gasifiers require a means for air and/or steam injection. Even the molten metal process has similarities to a variety of metal processing furnaces.
Could a system be built that is capable of doing both? Can we design a furnace that processes metals when market prices call for it while gasifying waste and biomass into renewable fuels or energy when the market leans in that direction? The FASTOX™ process suggests that we can because as a rule, anything that can be retrofitted can be un-retrofitted, or restored to its original condition. From a capital perspective, this possibility is huge. Capital financing is all about run-time and down-time. The more a given system runs, the more economical it becomes for financing. Systems that can easily be switched from one production capability to another are capable of higher run-time because they can adapt to economic conditions.
A key distinction of gasification compared to conventional coal plants is that the CO2 emitted in the process has generally been cleaned. Current gas separation technologies that are factored into the costs used in the estimates discussed here achieve a CO2 output that is 96% pure. This means that the CO2 can be used for other processes. While most plans focus on geologic sequestration, an intriguing possibility comes from a recent algae project.
The Florida company Algenol Biofuels is developing a process they call Direct To Ethanol®. This process feeds clean CO2 to hybrid algae in a specially designed bioreactor. Unlike other algae-based programs, these hybrid algae directly secrete ethanol that is evaporated in the bioreactor and is collected in channels by gravity. The system is completely sealed to prevent cross-breeding or contamination of the algae and the algae itself never leaves the bioreactor.
Three developmental projects are already in the works with output projections running from 6,000 gallons per acre per year to as much as 10,000 gallons per acre per year when enough CO2 is provided. This is compared to about 400 gallons per acre per year for corn-based ethanol and about 900 gallons per acre per year for sugar cane ethanol. If this technology works as currently projected, the available CO2 from the proposed infrastructure would be sufficient to produce a total of 1.6 billion barrels of ethanol per year. In the real world, we’d never be able to achieve that overall level of efficiency however even if only 60% of that is achievable it would make a huge impact, especially when one considers that the primary ingredient is waste CO2 gas. Overall, the process consumes 90% of the CO2 inserted into the system.
Other options exist for using clean CO2 as well. Other types of algae energy programs also generally need a supply of clean CO2, especially in designs using bioreactors. In areas where it is economically feasible to produce hydrogen via electrolysis, the CO2 and hydrogen can be reformed into additional synthetic fuels such as methanol. There are many uses outside of energy production for clean CO2 as well. In its solid and liquid forms, CO2 is an effective and environmentally sound refrigerant. As a gas, it is useful in welding and laser applications. It can be used in portable pneumatic systems as well as fire extinguishers. It also has applications in the food, beverage, and pharmaceutical industries. Consequently, concerns over the quantities of CO2 this gasification program could potentially produce should not be an issue. As long as it is properly cleaned and captured, the CO2 can be put to use in other functions instead of being blindly dumped into the atmosphere.