Flue Gas Emission

There are five primary pollutants found in the flue gas nitrogen oxides, carbon monoxide, sulfur oxides, imbumed hydrocarbons, and particulates. These components are formed during the combustion process. 

A NOx removal system may be required to meet a site s emission requirements. The typical system used for this case is a Selective Catalytic Reduction unit (SCR). The SCR unit reduces NOx by reacting armnonia with the flue gas over a catalyst, which yields nitrogen and water vapor. An SCR 

The CO, combustion produced particulates, and the unbumed hydrocarbons are all related to the amount of excess air, type of fuel, and the amount of mixing of the fuels within the burner. Insufficient air and inadequate mixing can result in incomplete combustion thus raising the amount of CO and unbumed hydrocarbons in the flue gas. Particulates formed in the combustion process are very low for gaseous fuels but will increase with the use of liquid fuels. 

The sulfur oxides that are formed are directly related to the amount of sulfur found in the fuel. These emissions are typically low when PSA offgas is burned with natural gas. The PSA offgas is sulfiir-free due to feedstock pretreatment to protect catalyst beds within the hydrogen plant. Natural gas also typically contains very low levels of sulfur. However, if refinery fuel gases are used as a makeup fuel to the reformer, then the sulfur emissions can increase dramatically as these streams often eontain large amounts of sulfur. 

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Air emissions from coking operations include the process heater flue gas emissions, fugitive emissions, and emissions that may arise from the removal of the coke from the coke drum. The injected steam is condensed and the remaining vapors are typically flared. Wastewater is generated from the coke removal and cooling operations and from the steam injection. In addition, the removal of coke from the drum can release particulate emissions and any remaining hydrocarbons to the atmosphere. 

As with boiler plant waterside functions, a major operational fireside objective is to maximize efficiency and keep maintenance and related costs under close control. This means that all fuel system components, fireside, and heat transfer surfaces must be kept clean and in good working order. Also, the fuel delivery, combustion, and flue gas emission processes should run equally perfectly. 

In any case, whether emissions are wet or dry, the presence of soot in the flue gas effectively means lost Btus. Where fuel treatments are employed, their function is to limit the supply side of flue gas emissions by improving the combustion process. 

The major emissions from the combustion of fuel are C02, SO, NO and particulates14. The products of combustion are best minimized by making the process efficient in its use of energy through efficient heat recovery and avoiding unnecessary thermal oxidation of waste through minimization of process waste. Flue gas emissions can be minimized at source by ... 

Smith R and Delaby O (1991) Targeting Flue Gas Emissions, Trans IChemE, 69A 492. 

The objectives of Aho s study [8] were to investigate the effects of peat type, particle density, diameter and moisture content, and oxygen concentration on the flue gas emissions of nitrogen oxides and sulphur dioxide from a homogenous countercurrent batch bed combustion using a pot furnace. His aim was to simulate the interaction of chemistry between the fuel bed system and the combustion chamber of a overfired batch bed. However, he also presented some results on the combustion heat rate. 

The zero-emission energy recycling system (ZEROS) is a closed-loop thermal oxidation process that incinerates waste and recycles flue gas emissions for electrical co-generation. The technology uses a two-stage plasma torch combustion system, energy recovery system, and combustion gas cleanup systems. 

However, 2,3-benzofuran was detected in emissions from a Swedish floor finish used on domestic flooring (van Netten et al. 1988), and in emissions from the pyrolysis of silk (Junk and Ford 1980), and in combustor flue gas emissions from fluidized-bed coal combustion at a concentration of 900 ng/g (Hunt et al. 1982). Exhaust produced by an automobile burning simple hydrocarbon fuels contained 2,3-benzofuran at concentrations ranging from less than 0.1 to 2.8 ppm (Seizinger and Dimitriades 1972), but an analysis of air in a highway tunnel in use by both diesel- and gasoline-powered vehicles indicated no... 

The CEN/TC 295 draft standard prEN 13240 [1] is based on measurements of efficiency and flue gas emissions at a nominal burning rate. The emission factors are based on concentration measurements of the pollutants in the due gas. The efficiency is calculated indirectly by the flue loss method taking into account the thermal due gas losses (sensible heat) and the chemical losses (combustible gases, here as carbon monoxide, CO). 

ISO/DIS 13336, Draft International Standard (DIS), Solidfuel burning appliances - Test method for determining power output, efficiency and flue gas emissions. International Organization for Standardization (1997)... 

The flue gas emissions are indicated as concentration based on a given value of oxygen in the exhausts (e.g. vol 13%) and as emission factors as mass per unit fuel based on dry with ash. The calculations of the gas concentration figures are based on the CEN/prEN test standards e.g. 13240. The calculations for the emission factors arc new and need to be defined. 

A variety of cogeneration processes has been recently described in the literature. A brief list is shown in Table 10.2, where representative examples involving porous materials and different types of fuel cells are included. In most cases, electrocogeneration allows for a simultaneous removal of organic pollutants and flue gas emissions. Examples of this possibility will be treated in Chapter 12. 

The sources of informafion used to evaluate burner performance on commercial scale insfallafions fypically falls into one of three categories (i) combustion performance in the oxy-fuel fired zone, (ii) flue gas emissions from the furnace (including any parficulafe maffer), and... 

From this brief discussion it is apparent that the effective use of mechanical cleaning of condensers to reduce the effects of biofouling, is well established. The use of higher grade fuels and the need to reduce detrimental effects on the environment fi om the use of chemicals and additional flue gas emissions, will encourage the installation of the technology. 

Consumption and emission data per tonne of good casting for a 3 t/h shaft furnace, melting aluminium are given in Table 3.22. This also gives the flue-gas emission levels of the raw offgas without cleaning. 

However, emissions are highly variable and depend on gasifier type, feedstock, process conditions (temperature and pressure), and gas conditioning systems. For example, indirect gasification systems generate flue gas emissions from the combustion of additional fuel, char, a portion of the feedstock. 

Table 12. Flue gas emissions during combustion of phenolics (data from ref. [257]) ...

Flue gas Emissions NO emission is an important environmental issue for the process industry today. The NO is formed by nitrogen and oxygen reacting at the peak temperatures of the flames. A standard gas burner produees 100 ppm NO premixed gas burner 80 ppm staged gas burners 40 ppm ultralow NO gas burners 30 ppm and the latest generation ultralow NO gas burners produce 8-15 ppm NO . SOx is controlled by the sulfur in the fuel. Many plants have sulfur limits that require burning low sulfur fuel oil. Carbon monoxide (CO) should be less than 20 ppm. 

Holmes MJ, Redinger KE, Evans AP, Nolan PS. Control of mercuiy in conventional flue gas emissions control systems, in Fourth international conference on managing hazardous air pollutants, Washington, DC, November 12-14, 1997. 

Smith, R. and Delaby, O., 1991, Targeting flue gas emissions, Trans IchemE, 69. 

Coal gasification combined cycle plants will meet the restrictions on the emission of trace components, hazardous air pollutants, or toxics. The CAAA lists 189 chemicals which would be subject to control at those sources within a contiguous area which emit 10 tons or more per year of any one pollutant or 25 tons or more per year of any combination of the pollutants. At least 36 of the 189 listed chemicals (see Table 4-8) have been found in utility flue gas emissions (29). Based on the levels of chloride commonly found in U.S. coals, HCl emissions could place many coal-fired power plants into the category of affected sources that exceed the 10 ton per year limit. 

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