Tail gas incinerator

Off-gas from the coke burner ( -Gas) contains nitrogen, sulphur dioxide (SO2), hydrogen sulphide (H2S), carbon monoxide (CO), carbon dioxide (CO2), water vapour and other trace contaminants. The -Gas is directed to the CO Boiler for incineration where sulphur compounds are converted to SO2. The Boiler flue gas is passed through electrostatic precipitators for particulate control and then emission to atmosphere. The CO Boiler also serves as the Sulphur Plant tail gas incinerator. Maximum sulphur emissions are 146 tonnes/day or 10.6% of sulphur contained in bitumen feed to the cokers. 

Economics Turnkey cost including tail gas incineration, Gulf ... 

For NGL plants, emissions usually come from gas sweetening units when acid waste gas is burned or incinerated. Most frequently, the acid waste gas is used as a feedstock in sulphur recovery units or in sulphuric acid plants. While flaring is often expected in NGL plants, the major poison and pollutant of concern is S02- Most plants employ elevated smokeless flares or gas incinerators for combustion of all waste gas constituent, including tail gas incinerator in which H2S is oxidized to SO2 (Berkel, 2000) [7]. Such practices are not sustainable. CP can be implemented to reduce and/or eliminate gas flaring or incinerations beyond acceptable level as stipulated by local environment authorities. 

The above SRU, designed on the basis of modified Claus process, is equipped with a tail gas Incinerator of natural draft, sub-atmospheric pressure type thermal incinerator with air flow controlled using burner air registers. Tail gas inlet line to the incinerator is installed with a Tied Universal type metallic bellow expansion joint to accommodate line expansion and movements. This expansion joint made out of Inconel-65 metallurgy was in operation since Year 2005 which subsequently during May-2011 had developed a crack on the metallic bellow element and started leaking toxic tail gas to atmosphere. 

Waste gases contsdning liquids that must be disposed of and that for environmental or safety reasons cannot be directed to the flare system are burned in a tail gas incinerator, shown in Exhibit 7-50. The horizontal in-... 

Tail gas containing traces of SO2, H2S, COS and CS2 are usually sent to a finishing processing before being incinerated. 

Other developing or potential appHcations for lime are neutralization of tail gas from sulfuric acid plants, neutralization of waste hydrochloric and hydrofluoric acids and of nitrogen oxide (NO ) gases, scmbbing of stack gases from incinerators (qv), and of course, from small industrial coal-fired boilers. 

There are many processes used in tail-gas treating. The Sulfreen and the Cold Bed Absorption (CBA) processes use two psirallel reactors in a cycle, where one reactor operates below the sulfur dew point to absorb the sulfur while the second is regenerated with heat to recover molten sulfur, tiven though sulfur recoveries with the additional reactors are normally 99-99.5% of the inlet stream to the Claus unit, incineration of the outlet gas may still be required. 

Low-temperature activity promotion is an issue in mobile (diesel) applications, but may not be a critical issue in several stationary applications, apart from those where the temperature of the emissions to be treated is below 200°C (for example, when a retrofitting SCR process must be located downstream from secondary exchangers, or in the tail gas of expanders in a nitric acid plant). In the latter cases, a plasmacatalytic process [91] could be interesting. In the other cases, the use of NTP together with the SCR catalyst is not economically viable. However, the synergetic combination of plasma and catalysts has been shown to significantly promote the conversion of hazardous chemicals such as dioxins [92], Although this field has not yet been explored, it may be considered as a new plasmacatalytic SCR process for the combined elimination of NO, CO and dioxins in the emissions from incinerators. 

Elsewhere in this review we have commented on the problem of COS production as a result of high temperature reactions occurring in the front end furnace. Sulfur in this form is not subject to conversion to elemental sulfur in the catalytic redox Claus reaction and thus appears as COS in the tail gas where it is incinerated to SO2 thus adding to losses to the environment. The COS and any CS2 can be hydrolyzed to H2S which can then be converted by the redox Claus reaction. 

Recent developments in desulfurizing the effluents from sulfur plants have concentrated on the plant tail gas before incineration. This avoids the further dilution of the effluent stream with nitrogen from air used as the oxidant and many of the sulfur values are still in a reduced or at least unoxidized state. 

Environmental regulations may force the "Claus" sulfur recovery to exceed 99%, requiring tail gas treatment. High CO2 in the original Claus feed, hence in the Claus tail gas, works strongly against the tail gas processes which use amine solution to extract H2S, and subsequently require incineration of residual H2S in a large volume of CO2. 

Continuous tail gas analyzers provide information on flow rates and H2S S02 ratios which is used to control operation. As indicated previously, the tail gases are routed to the CO Boiler for incineration before emission to atmosphere via the main stack. 

The H2S concentration in the tail gas of a conventional Claus plant is still some 5%. This H2S is normally incinerated to S02 and released to the atmosphere. Due to stricter environmental regulations a large number of new technologies based on Claus tail gas treatment have been developed to minimise the S02 exhaust from sulphur recovery units. The Superclaus process and the Shell Claus Off-Gas Treating (SCOT) process are treated below. For descriptions of other tail-gas processes, the reader is referred to [2],... 

The SCOT process provides an efficient way of removing sulphur-containing compounds from the tail gas of a conventional Claus reactor. The tail gas is heated to about 300°C and fed to a hydrogenation reactor, where all sulphur compounds in the gas are converted to H2S. Almost all H2S is removed in an absorber/stripper combination and fed back to the Claus plant. The off-gas from the absorber contains virtually no sulphur compounds (values as low as 500 ppm are reported [2]) and is incinerated in the Claus incinerator. A schematic diagram of the SCOT process is provided in Figure 2. 

Figure 25.4 shows a typical sulfur recovery plant based on the Claus process. The tail gas from the Claus reactors may be further processed to remove any remaining sulfur compounds. Combined H2S removal efficiencies of 99.5-99.99 percent are achievable.20 This may be done by low-temperature Claus-type solid-bed processes (e.g., the Sulfreen process), wet-Claus absorption/oxidation processes (e.g., the Clauspol 1500 process), or hydrogenation of the off-gas to form H2S for recycle (e.g., the SCOT process). Residual sulfur compounds in the tail gas are then incinerated to S02. The residual S02 in the oxidized tail gas may be scrubbed by any of several processes (e.g., the Wellman-Lord process) before being vented to the environment. It is feasible to bring the H2S content of... 

In the absorber, the formaldehyde is absorbed in water or urea solution. Heat is removed by one or two cooling circuits (8, 9). From the lower circuit (8), product in the form of either AF or UFC is withdrawn. Scrubbed gas from the absorber is split in two streams—recycle gas and tail gas. The tail gas is vented after any organic impurities are catalytically incinerated in the reactor (10). Thus, the tail-gas purity conforms to the environmental standards for any country. 

The effluent streams from Claus plants contain unreacted hydrogen sulfide and sulfur dioxide and elemental sulfur present as vapor and mist (77). They commonly also contain carbonyl sulfide and carbon disulfide formed by reactions with hydrocarbons present in the feed gas (77). It is usually required that the tail gas be incinerated, even though not otherwise treated, to convert the hydrogen sulfide, carbonyl sulfide, and carbon disulfide to the less toxic and malodorous sulfur dioxide. 

Incineration of the tail gas and conversion of all sulfur compounds to sulfur dioxide, followed by one of the sulfur dioxide control systems. 

Economics. The capital investment for a Beavon plant to process tail gas from a 100-long-ton/day Claus unit is about 1,250,000. Operating costs for a unit of this size are given in Table I. The fuel and steam required by the process is less than one-fourth of that required for simple incineration. Should fuel gas cost increase to 2/MM Btu as has been forecast, the energy savings would make the operation profitable. 

Protection against contamination of the amine by small amounts of sulfur dioxide is provided by the reaction of sulfur dioxide with hydrogen sulfide to form sulfur in low temperature Claus reaction in the water phase. The quench water itself provides very sensitive early warning of potential trouble from sulfur dioxide breakthrough, and proper instrumentation can sound an alarm and/or divert the SRU tail gas to the incinerator until the breakthrough is corrected. These indicators are color, pH, and turbidity, in order of increasing situation severity. With proper instrumentation the amine should never be contaminated. 

Tail gas to fuel use or incinerator with steam generation... 

Caution is necessary to avoid condensation of an aqueous phase in the system because of the extreme corrosive nature of the liquid phase. Another operating issue concerns mist formation, a phenomenon which occurs very readily when condensing sulfur, and a series of demisters are necessary to prevent this. Residual sulfur is converted to sulfur dioxide by incineration of the tail gas from the process to prevent emission of other sulfur compounds and to dilute the effluent to reduce ground level sulfur dioxide concentrations. 

In the Claus process Sulphur Recovery Units, metallic bellow expansion joints in the tail gas line to Incinerator, seldom fail by developing crack on the bellow element due to various mechanical and metallurgical reasons. 

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