There are several types of gasifier designs. None have smokestacks. Click the pic for more info about this image.
Gasification was first developed in the 1800s and has been used commercially throughout the world for over a century. A variety of industries utilize the technology including chemical production, fertilizer manufacturing, and electric power generation. Today, the majority of operating gasification plants produce chemicals, fuels, electricity, and fertilizers. Here’s a map of known gasification projects worldwide.
The most common misconception of gasification is the assertion that “gasification is just another name for incineration.” Modern gasifiers do not have a smokestack, while all incinerators have stacks. There are more than 30 different makes and models of gasifiers available for a wide range of applications, ranging from pyrolysis (incomplete) gasification designs used to convert biomass into biochar or convert shredded tires into synthetic diesel fuel, to extra-clean smokestack-free gasifiers that cleanly gasify coal, municipal solid/liquid wastes, hazardous wastes, and sludges. There are significant differences in the various gasifier designs, emissions and ranges of feedstocks, as well as scalability.
While incineration and gasification technologies are similar, the energy resource from incineration is high-temperature heat, whereas the main energy resource from gasification is intermediate synthetic gas (CO, H2 syngas) which can either be combusted to produce electric power or cleanly converted via gas-to-liquid (GTL) catalysis into liquid fuels and a variety of chemical compounds.
In gasification either a single feedstock or multiple types of feedstock are converted by high temperature into its constituent elements, primarily Carbon, Oxygen and Hydrogen. The process is commonly referred to as molecular dissociation. Conversion conditions are carefully controlled so that prior to exit, nearly all of the carbon elements reform into the desired CO and H2 syngas. Non-carbonaceous materials which cannot be converted into syngas, such as metal, glass, rock, sand, dirt or concrete, are slagged out as either ash, or a molten pour of obsidian-like, inert vitreous glassy slag. Such glassy slag can be safely landfilled as it will never leach. Extra-strong slag also has multiple commercial uses as an abrasive element, repairing potholes in roads being just one application.
A number of factors contribute to growing interest in gasification, including volatile oil and natural gas prices, more stringent environmental regulations, and a growing consensus that CO2 management should be required in power generation and liquid fuel production.
More info: Gasification Technologies Council: Gasification: An Investment In Our Energy Future (PDF)
Large or small, every type of combustion incinerator has a smokestack.
Incineration is the waste management industry’s current solution for converting municipal solid waste into electricity. Virtually all currently operating waste-to-energy facilities are incinerators. There are over 450 operating incinerators in western Europe, while the U.S. EPA estimates that there are currently approximately 176 industrial waste incineration units, including incinerators, small remote incinerators, burn-off ovens, waste-burning cement kilns and energy recovery units.*
* Source: U.S. EPA. “Standards of Performance for New Stationary Sources and Emission Guidelines for Existing Sources: Commercial and Industrial Solid Waste Incineration Units, Proposed Rule.”
Incinerators must vent byproducts of combustion (C02, H20, CO, NOx, SOx, microscopic particulates, etc.) in order to function. An incinerator is essentially a smokestack with a fire at the bottom, with scrubbers at the top to extract the worst pollutants but send the rest to the atmosphere. In incineration, excess O2 is added to the input waste so that at low temperature it burns. The result is heat and an exhaust of CO2, H2O and other byproducts of oxidation combustion or partial combustion, including poisonous dioxins and furans. As much as 30% of the processed solid waste remains as ash. This ash could be categorized as hazardous solid waste.
Gasification is inherently superior technology for converting all types of solid and liquid wastes and fossil carbon feedstocks to clean, intermediate syngas, which can then be converted electric power or liquid fuels, without emitting toxic compounds or CO2 or requiring supplementary fossil fuel. Gasification technologies in combination with Gas to Liquid (GTL) fuel synthesis architecture represent the future of environmentally responsible waste management and extra-profitable liquid fuel production.