Combustion unit

Whenever unvented combustion occurs iadoors or when venting systems attached to combustion units malfunction, a variety of combustion products win be released to the iadoor environment. Iadoor combustioa units include nonelectric stoves and ovens, furnaces, hot water heaters, space heaters, and wood-burning fireplaces or stoves. Products of combustion include CO, NO, NO2, fine particles, aldehydes, polynuclear aromatics, and other organic compounds. Especially dangerous sources are unvented gas and kerosene [8008-20-6] space heaters which discharge pollutants directly into the living space. The best way to prevent the accumulation of combustion products indoors is to make sure all units are properly vented and properly maintained. 

Another type of combustion unit operates at about 1600°C to produce a molten slag which forms a granular frit on quenching rather than the usual ash. The higher operating temperature is obtained by preheating the combustion air or by burning auxiUary fuel. 

Nitrous gases originating from the combustion units in nitric acid plants carry small amounts of unreacted ammonia, NH3. The ammonia may react with the nitrous gas to form microscopic particles of ammonium nitrate that adhere to solid surfaces. Within a short time, there is a growing layer of ammonium nitrate salt covering the internal surface of the nitrous gas compressor (Figure 4-27). This layer can obstruct the flow passages because it tends to increase the power consumption, provoke excessive vibrations, and even present a safety hazard since ammonium nitrate explosions can occur. 

Direct hydrogen cyanide (HCN) gas in a fuel oil gasification plant to a combustion unit to prevent its release. 4. Consider using purge gases from the synthesis process to fire the reformer strip condensates to reduce ammonia and methanol. 5. Use carbon dioxide removal processes that do not release toxics to the environment. When monoethanolamine (MEA) or other processes, such as hot potassium carbonate, are used in carbon dioxide removal, proper operation and maintenance procedures should be followed to minimize releases to the environment. 

Fossil-fuel and wood-waste fired industrial and commercial fuel combustion units commonly use multiple cyclones (generally upstream of a wet scrubber, ESP, or fabric filter) which collect fine PM (< 2.5 im) with greater efficiency than a single cyclone. In some cases, collected fly ash is reinjected into the combustion unit to improve PM control efficiency (AWMA, 1992 Avallone, 1996 STAPPA/ALAPCO, 1996 EPA, 1998). 

Figure 14-39. Gas turbine combustion unit. (Used by permission Westinghouse Electric Corporation.)...

Since most of the regenerators operating in full combustion mode usually operate with 1 % to 3% excess oxygen, the capturing efficiency of SOj - additive is often greater in full combustion than in partial combustion units. 

This type includes solar pans and submerged combustion units. Submerged combustion evaporators can be used for applications where contamination of the solution by the products of combustion is acceptable. 

Hazardous wastes are combusted for various purposes. The purpose of combustion is directly related to the type of unit used. There are two classes of combustion units, those that burn waste for energy recovery and those that burn waste for destruction. 

The second class of combustion units is BIFs. Boilers are used to recover energy from hazardous waste, whereas industrial furnaces are used primarily to recover material values. 

Emissions from combustion units may comprise a variety of hazardous pollutants. To minimize potential harmful effects of these pollutants, U.S. EPA developed performance standards to regulate four pollutant categories ... 

The combustion unit must demonstrate a DRE of 99.99% for each POHC in the hazardous wastestream. This means that for every 10,000 molecules of the POHC entering the unit, only one molecule can be released to the atmosphere. In addition, due to an increased threat to human health and the environment posed by certain dioxin-containing wastes, the required DRE for POHCs in these units has been established at 99.9999%, or one released molecule for every one million burned. These DRE standards must be met by both incinerators and BIFs. 

Hydrogen chloride and chlorine gases form when chlorinated organic compounds in hazardous wastes are burned. If uncontrolled, this chlorine can become a human health risk and is a large component in the formation of acid rain. U.S. EPA has developed different requirements to control the emissions of chlorine from the different classes of combustion units. 

The final performance standard is for toxic metals. For RCRA combustion units, both carcinogenic and noncarcinogenic metals are regulated under the same type of tiered system as chlorine. The facility determines an appropriate tier for each regulated metal and assures that the facility meets these feed rate and emission standards. A different tier may be selected for each metal pollutant. 

U.S. EPA may require owners and operators of hazardous waste combustion units to comply with additional performance standards by virtue of the omnibus authority. This authority allows U.S. EPA to incorporate additional terms and conditions into a facility s permit as necessary to protect human health and the environment. 

U.S. EPA recommends that site-specific risk assessments, incorporating direct and indirect exposures, be considered during the combustion unit s permitting process. These risk assessments may be used to evaluate the unit s impact on the surrounding environment. If a site-specific risk assessment shows that additional protection should be afforded to the surrounding environment, U.S. EPA typically will use the omnibus authority to impose the necessary permit conditions. 

The goal of setting operating requirements for hazardous waste combustion units is to ensure that the unit will operate in a way that meets the performance standards for organics, chlorine, particulate matter, and metal pollutants. The unit s permit will specify the operating conditions that have been shown to meet the performance standards for organics, chlorine gas, particulate matter, and metals. 

An RCRA permit for a hazardous waste combustion unit sets operating requirements that specify allowable ranges for, and requires continuous monitoring of, certain critical parameters that will ensure compliance with the performance standards. Operation within these parameters ensures that combustion is performed in the most protective manner and the performance standards are achieved. These parameters, or operating requirements, may include... 

To control the emission of organics, these units must comply with similar DRE requirements to the other hazardous waste combustion units. Owners or operators of MACT combustion units must select POHCs and demonstrate a DRE of 99.99% for each POHC in the hazardous wastestream. Sources that bum hazardous waste have a required DRE of 99.9999% for each POHC designated. Additionally, for dioxins and furans, U.S. EPA promulgated more stringent standards under MACT. For example, MACT incinerators and cement kilns that bum waste with dioxins and furans must not exceed an emission limitation of either 0.2 ng of toxicity equivalence per dry standard cubic meter (TEQ/m3) or 0.4 ng TEQ/m3 at the inlet to the dry particulate matter control device. This unit of measure is based on a method for assessing risks associated with exposures to dioxins and furans. 

Rather than a tiered system to control hydrogen chloride and chlorine gas emissions, MACT combustion units must meet numerical emission limits for total chlorine. Owners and operators of these units must ensure that the total chlorine emission does not exceed specific limits, expressed in ppmv. For example, the allowable limit of total chlorine for a new incinerator is 21 ppmv. The owner or operator may choose to achieve this level by controlling the amount of chlorine entering the incinerator. By achieving the regulatory emission limit of chlorine, both hydrogen chloride and chlorine gas emissions will be reduced. 

U.S. EPA developed more stringent standards for particulate matter in order to control certain metals. This surrogate is used because particulate matter may provide a point of attachment for toxic metals that can escape into the atmosphere from a combustion unit. For instance, a new LWAK cannot exceed an emission limit of 57 mg/m3 of dry particulate matter. 

The facility may also choose to use an advanced type of monitoring known as continuous emissions monitoring systems (CEMS). CEMS directly measure the pollutants that are exiting the combustion unit stack at all times. If a facility chooses to use a CEMS, they do not need to comply with the operating parameter that would otherwise apply. 

Because hazardous waste combustion units are a type of TSDF, they are subject to the general TSDF standards in addition to combustion unit performance standards and operating requirements. Combustion units are also subject to specific waste analysis, inspection and monitoring, and residue management requirements. 

Conducting visual inspections of the combustion unit and its associated equipment. 

Residues from the combustion of hazardous waste are also potentially subject to RCRA regulation. If a combustion unit bums a listed hazardous waste, the ash could also be considered a listed waste via the derived-from rule. The owner and operator must also determine whether this ash exhibits any hazardous waste characteristics. The same is true if a unit bums waste that only exhibits a characteristic. Ash that exhibits a characteristic must be managed as a hazardous waste. 

At pulp and paper mills, air emissions from both process and combustion units are regulated under the National Ambient Air Quality Standards (NAAQS) and the State Implementation Plans (SIP) that enforce the standards. States may implement controls to limit emissions of particulate matter (PM), nitrogen oxides (NO ), volatile organic compounds (VOCs), and sulfur dioxide (S02). 

There are two categories of combustion units for solid and liquid hazardous wastes ... 

Figure 23.1 provides a compilation of information on reported emergency incidents at hazardous waste combustion facilities and other TSDFs regulated under the RCRA. It covers emergency incidents such as fires, explosions, hazardous waste spills, or unauthorized releases of hazardous waste. The reported incidents at 24 hazardous waste combustion units and 26 other TSDFs... 

While most incinerators must undergo a trial burn, it is possible for a facility to submit extensive information in lieu of the trial burn. U.S. EPA believes that most combustion units will need to conduct trial burns in order to develop operating conditions that ensure compliance with the performance standards. Data submitted in lieu of the trial burn, therefore, must originate from a unit with a virtually identical design that will burn wastes under virtually identical conditions (i.e., located at the same facility). 

While most BIFs must undergo a trial burn, it is possible for a facility to submit extensive information in lieu of the trial burn. U.S. EPA believes that most combustion units will need to conduct... 

Metal bearing waste prohibited from dilution in a combustion unit according to 40 CFR 268.3(c)... 

In power stations or other combustion units above a capacity of, say, 1 MW, UV sensors for flame monitoring are not unusual. Here, even combustion parameters like the air or fuel supply are controlled by sensing the UV emission spectrum of the flames. 

Fig. 7.11 On-line GC-combustion unit for isotope ratio determinations (Ghosh, P. and Brand,...

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