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Federal Register / Vol. 86, No. 171 / Wednesday, September 8, 2021 / Proposed Rules
hydrocarbon bonds of the incoming feed materials and may generate tars, oils, particulate matter, reduced sulfur and nitrogen compounds, and hazardous air pollutants HAPs including polycyclic aromatic hydrocarbons PAHs.

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2. Gasification Units Gasification is a process of converting feed materials primarily carbonaceous into syngas carbon monoxide and hydrogen and carbon dioxide. The materials are gasified when they react with controlled amounts of oxygen or steam at high temperatures greater than 700 C. Oxygen as air, concentrated oxygen, or steam is added in small amounts to maintain a reducing i.e., oxidation or combustion-preventing atmosphere, where the quantity of oxygen available is less than the stoichiometric ratio i.e., amount needed for complete combustion of the feed material. The process of gasification has endothermic and exothermic 10
phases, but overall is an exothermic process and requires an external heat source, such as syngas combustion, char combustion, or steam. Gasifiers have a wide variety of types and designs, but there are four major classifications: 1
Updraft fixed bed gasifier, 2 downdraft fixed bed gasifier, 3 bubbling fluidized bed gasifier, and 4 circulating fluidized bed gasifier.11 In updraft gasifiers, which are the oldest designs, feed materials enter from the top of the gasifier and oxygen and/or steam are injected at the bottom; this is referred to as counterflow gasification. Updraft gasification can reach temperatures above 1,200 C. Downdraft gasifiers generally are configured like updraft gasifiers, but rely on co-current flow, and feed materials and reactants oxygen and steam flow in the same direction within the reactor.12 Like updraft gasification, downdraft gasification can reach high temperatures. Bubbling fluidized bed gasifiers mainly are used to convert materials to syngas. These units typically contain a bed made with inert particles of sand or alumina interspersed with several air or steam nozzles on the reactor floor. Oxygen and/or steam are injected through the nozzles into the bed and create bubbles as they move through the feed materials, leading to more uniform heat 10 Exothermic is a process where heat is produced by a chemical reaction, thus resulting in elevated temperature.
11 Benchmarking Biomass Gasification Technologies for Fuels, Chemicals and Hydrogen Production, Prepared for U.S. Department of Energy, National Energy for Technology Laboratory, by Jared P. Ciferno and John J. Marano, 2002.
12 Ibid.

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distribution throughout the reactor and a higher conversion rate from feed materials to syngas.13 Circulating fluidized bed gasifiers are in many ways very similar to bubbling fluidized bed gasifiers but are capable of higher gas velocities and throughput by capturing and recirculating the bed medium.
These gasifiers may lead to faster reaction and a higher conversion rate.
Syngas, the primary product of gasification, is a fuel and can be burned in boilers, gas engines, or turbines. It can also be used as a chemical feedstock to produce other, more complex chemicals or hydrocarbon fuels. Often, a gasification agent such as steam is added to enhance the fuel value of syngas because steam reacts with carbon monoxide to produce additional hydrogen. Hydrogen may be used as a feedstock or used in fuel cells or hydrogen turbines. Additionally, gasification facilities may use a process, knowns as the Fischer-Tropsch process, where syngas converts, in the presence of metal catalysts at 150300 C and high pressures, into liquid hydrocarbon fuel.
B. What is the regulatory background for pyrolysis and gasification units?
As noted previously, there is some difference in the treatment of pyrolysis units among the EPAs existing CAA
section 129 rules. CAA section 129
relates to standards for various categories of solid waste incineration units. Some of the EPAs CAA section 129 rules do not mention pyrolysis or gasification at all, while others contain specific language applicable to certain types of units or processes. The rules for MWC, for example, generally define municipal waste combustion units or municipal waste combustor units to include pyrolysis/combustion units see, e.g., 40 CFR 60.51a; 40 CFR
60.1465 but exempt such units that are integrated parts of a plastics/rubber recycling unit under certain circumstances. see, e.g., 40 CFR
60.50ak; 40 CFR 60.1020h. With some difference in language, these rules essentially define pyrolysis/
combustion units as units that produce gases, liquids, or solids through the heating of MSW, and the gases, liquids, or solids produced are combusted and emissions vented to the atmosphere see, e.g., 40 CFR 60.51a and 60.1465.
The HMIWI rules, by contrast, define pyrolysis to mean the endothermic gasification of hospital waste and/or medical/infectious waste using external energy see, e.g., 40 CFR 60.51c and provide that pyrolysis units are not 13 Ibid.

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subject to the HMIWI rules see, e.g., 40
CFR 60.50cf. The EPA discussed pyrolysis in a June 20, 1996, proposal relating to the HMIWI standards 61 FR
31736. In the September 15, 1997, final rule 62 FR 48348, the EPA deferred development of standards for pyrolysis units and determined that the HMIWI
standards were not appropriate for pyrolysis units. In discussing pyrolysis, the EPA stated, Pyrolysis technology is different from conventional incineration. Because air is generally not used in the pyrolysis treatment process, the volume of exhaust gas produced from pyrolysis treatment is likely to be far less than the volume of gas produced from the burning of waste in an HMIWI. Although conventional combustion does not occur during pyrolysis treatment, there are some emissions from the pyrolysis process.
62 FR 48358. The EPA also noted difficulties with attempting to modify the HMIWI regulations to apply to pyrolysis units; asserted that sufficient information was not available to develop a separate and uniform regulation for pyrolysis; and noted that EPA may consider these devices in future regulatory development Id. at 48359.
The Agency also notes that there is no definition of pyrolysis/combustion units in the NSPS and EG for CISWI
units and SSI units, and no definition of gasification units in any of the NSPS
and EG discussed in this section.
The current rules for OSWI units define municipal waste combustion unit to include pyrolysis/combustion units without defining pyrolysis/
combustion units see, e.g., 40 CFR
60.2977. On August 31, 2020, the EPA
published a proposed rule in the Federal Register for the OSWI standards that, in part, proposed to remove pyrolysis/combustion units from the definition of municipal waste combustion unit. In that proposal preamble, the EPA stated that the term pyrolysis/combustion units is not defined in the current regulation and there is no similar specific reference to such units in the institutional waste incineration unit definition 85 FR
54178, 54187. The Agency also noted that the definition of solid waste in the OSWI rules included contained gaseous material defined as gases that are in a container when that container is combusted resulting from certain activities and asserted that the combustion of uncontained gases in pyrolysis/combustion units is inconsistent with such definition. Id.
The EPA also added that unlike combustion, the pyrolysis process is endothermic and does not require the
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