How Does FastOx Gasification Work?
A description of FastOx gasification.
FastOx Gasification Overview
FastOx gasifiers employ a fixed-bed system that breaks down waste at the molecular level. Waste is fed into the top of the gasifier vessel through an airlock. Purified oxygen and steam are injected into the base. The gasification reaction occurs at temperatures around 2,200°C (4,000°F). As the waste descends within the gasifier, it passes through several reaction zones reaching the hottest area at the base. In each zone, different materials are driven off. At the lowest point of the gasifier, the waste is reduced to carbon char, inorganic materials, and metals.
Injected oxygen and steam react with the carbon char to produce a synthesis gas (syngas), comprised predominately of carbon monoxide and hydrogen. This reaction is highly exothermic, meaning that it releases a large amount of energy in the form of heat. The syngas and heat rise through the gasifier, interacting with the waste as it descends through the vessel. Syngas exits the top of the gasifier vessel and into the heat recovery and gas cleaning isles.
At the base of the gasifier, inorganic materials and metals collect in a molten state. This molten liquid is periodically tapped out and cools into a vitrified stone that is very similar in appearance to volcanic rock and suitable for use in landscaping or as construction material aggregate.
A key innovation of FastOx gasification is the optimized rate and position of oxygen and steam injection into the gasifier. This drives the complete conversion of waste into its molecular constituents without the production of any major byproducts that require additional disposal. The ultra high temperatures and the use of purified oxygen (as opposed to nitrogen-rich ambient air) avoids greenhouse gas emissions because it eliminates nitrogen from the process and preventing the formation of harmful substances such as nitrogen oxides (NOx).
A complete FastOx system includes equipment for feedstock preparation, gasification, syngas conditioning, and final product conversion to fuels or energy.
How Does a FastOx Gasifier Work?
FastOx gasification can accept most waste, with the exception of radioactive and explosive materials. This includes municipal solid waste, biomass, construction and demolition waste, industrial waste, and even complex wastes, such as hazardous, toxic and medical wastes without any additional treatment requirements.
The FastOx gasifier requires minimal pre-treatment of feedstock. After waste material is delivered to the site, it is shredded prior to gasification. The gasfiier can handle wastes with moisture contents of up to 50% by weight although optimal moisture content is 20% and below.
Learn more about feedstock options.
The residence time of feedstock is controlled by the supply of injected oxygen and steam at the bottom of the gasifier. By injecting oxygen, FastOx gasifiers avoid the environmental impacts associated with blast furnaces that are caused by injecting ambient air, which consists mostly of nitrogen. Waste descends through the gasifier by gravity through four reaction zones:
1) Drying occurs in the top zone of the unit where hot syngas - produced at the bottom of the gasifier - rises and passes through the waste, driving off free moisture in the waste as it passes.
2) Devolatization is where the majority of the volatile matter is driven off into syngas. The volatile matter is typically where the large amount of the chemical energy in the waste is released as a mix of light gases, hydrocarbons, and condensable tars. These will be broken down into more syngas at high temperature or removed from the product syngas in the conditioning stages.
3) Partial oxidation occurs when the remaining carbon-containing materials in the waste (char/fixed carbon and ash) react with the injectants. This exothermic oxidation reaction produces high temperatures in the range of 2,200°C (4,000°F) allowing for the thorough conversion of remaining carbon into syngas. The energy produced at this stage allows FastOx gasification to be self-sustaining (no need to add heat).
4) Melting of inorganic compounds and metals results from the high temperatures occurring in the partial oxidation zone. These compounds collect at the bottom of the unit in a molten state and are continuously removed as inert stone and recycled metals.
Steam is co-injected with the oxygen, to maintain the flame temperatures within the blast furnace design parameters. The additional benefit of injecting steam is that it produces large volumes of hydrogen. This hydrogen can be used with CO to produce liquid fuels via catalytic processes or separated from the syngas to produce hydrogen fuel.
Syngas Cleaning and Conditioning
Syngas is produced from the top of the vessel and is moved to the cooling and conditioning processes. A heat exchanger removes excess heat from the producer syngas. This heat can be used to make steam for the system, which is recycled back into the steam isle and then injected into the gasifier as needed.
Syngas then goes into the gas-cleaning isle that removes particulates and gaseous contaminants to meet the requirements of downstream syngas-to-product conversion processes and to meet the local environmental air regulations for the project site. Clean syngas can then be converted to produce valuable end-products, such as electricity, renewable fuel, ethanol, crude oil substitute, hydrogen and more.
To generate electricity, syngas must be cleaned to the degree at which it can be used to power an electrical generation engine. The production of diesel, hydrogen fuel, and other end products, requires additional syngas cleaning efforts, as their impurity requirements are more stringent than that of electricity production. As a result, each desired end-product may require a unique syngas cleaning and conditioning process.
The production of renewable fuel is possible via a number of conventional catalytic technologies, such as the well-established Fischer-Tropsch (FT) synthesis process. This process converts syngas into renewable fuels by a series of chemical reactions over a catalyst. There are many companies that presently manufacture commercial-grade Fischer-Tropsch reactors, such as Rentech, Velocys, and Emerging Fuels Technology.
Biological back-end methods such as microbial fermentation, which utilizes microbes to generate gasoline and other chemicals, can also be applied. Companies such as LanzaTech, Coskata, INEOS Bio, and Kiverdi, have already commercialized these technologies.
FastOx Gasification Technology Advantages
FastOx gasification has several key advantages compared to other waste-to-energy technologies:
Simple, Robust Design
FastOx gasifiers are designed for continuous operation with few moving parts. Their simple design translates into low maintenance costs, efficient processing of waste and high system uptime.
Thorough Waste Conversion
The high temperature at which FastOx gasifiers operate ensures that all waste breaks down at the molecular level. Organic material is vaporized and collected as a clean syngas and inorganic material melts and is collected as metal and non-leaching vitrified stone. There are no major byproducts from the process that require additional disposal.
Flexible Waste Processing
FastOx gasifiers can handle nearly any waste including waste with high moisture content, with minimal pre-processing and no need to separate wastes. Suitable wastes include municipal solid waste, auto shredder residue, construction and demolition waste, medical waste, hazardous waste, industrial waste and biomass. Exceptions are radioactive or explosive wastes.
Minimal Land and Water Use
A FastOx system occupies far less land than other renewable energy technologies. While some water is needed to create steam and cool the system, moisture in the waste processed can be recovered and reused. For the same amount of energy, a FastOx system requires a fraction of the space needed for a solar array.
Low Capital and Operating Costs
The average FastOx system is 22% more cost-effective than competing technologies, both as to capital needs and operating costs over the life of the system. A low parasitic load (16-20%) also increases system profits.
Production of High Value Products
The syngas produced via FastOx gasification can be converted into a wide range of sustainable and salable energy products, including electricity, diesel, hydrogen, and ammonia. Each FastOx systems are designed to meet the specifications of each site.
FastOx Gasification Scale
At what scale can you design a FastOx gasifier?
Sierra Energy's commercial gasification system is designed to process a throughput of 20 tons per day. Due to the simplicity of the blast furnace technology, FastOx systems have the capability to reach capacities of up to 2,000 metric tons per day. Small increases to the gasifier diameter significantly raise waste handling capacity and thermal efficiency.
Is scaling up easy?
The FastOx® gasifier’s ‘specific consumption’ (material consumed per day per unit volume) is related to the volume of the vessel. Therefore, a small increase in gasifier diameter will significantly increase waste capacity as well as thermal efficiency. All of the related system components would also increase proportionally in size should scaling up be desired. The largest component to accommodate would be the storage space for feedstock/waste.
If scale-up of a particular plant/project is anticipated, Sierra Energy can adjust designs to accommodate the size increase with sufficient notice. In that case, additional diligence would be required during the design phase as well as attention to the capital required for larger equipment and change-out. If scale-up is not anticipated early in the design process, redesign would require additional engineering services to appropriately assess system modifications.
Scaling-up becomes increasingly challenging with systems over 100 MTPD capacity due to the codes and regulations involved in storing large quantities of gases on site.
What is needed to scale up?
The primary engineering considerations that must be considered in the event of a scale up are the increases in gasifier size and the assurance that gasifier support equipment (i.e. gas cleaning, oxygen/steam production, and back-end equipment) is capable of handling increased gas throughput. Scale up also must consider increase in capital outlay and future maintenance costs to ensure that the solution optimizes costs and profits.
The major modification to a FastOx gasifier in the event of a scale up is an increase in the diameter of the gasifier. This modification may require switching out an existing gasifier with a larger one.
Upstream and downstream equipment will vary as well depending on their particular specifications. Some equipment may need to be replaced with modules that can handle the increased capacity. However, costs associated with scaling-up can be minimized if Sierra Energy is notified earlier in the design process.
The exact needs for a scale-up operation will vary with each specific project and requires a cost-benefit analysis for the scaled up operation to ensure the appropriate solution is achieved. Contact Sierra Energy today for more information regarding your particular needs.