Atmospheric emissions reactor

Liquid nitrogen is used in cold traps to remove and recover solvents or volatile organic compounds from gas streams to reduce atmospheric emissions. Liquid nitrogen can be used to accelerate the cooldown time for process reactors (29). 

The introduction of solid catalysts into a traditionally non-catalytic free-radical process like combustion occurred in recent years under the influence of two pressures, the energy crisis and the increased awareness of atmospheric emissions. The major applications of catalytic combustion are twofold at low temperatures to eliminate VOC s and at high temperatures (>1000 C) to reduce NOx emission from gas turbines, jet motors, etc. Both these applications are briefly reviewed here. Some recent developments in high-temperature catalytic combustion are trend-setters in catalysis and hence of particular interest. For instance, novel materials are being developed for catalytic applications above 1000 C for sustained operation for over one year. Where material/catalyst developments are still inadequate, systems engineering is coming to the rescue by developing multiple-monolith catalyst systems and the so-called hybrid reactors. 

The combustion reaction is realized in the firebox of the waste heat boiler within the Claus unit, while the Claus reaction and hydrolysis reactions take place in the Claus reactor filled with a catalyst. This process requires two or three Claus reactors. The sulfur recovery is 90%-96% in the first two reactors and is 95%-98% in the third reactors. Recently, super-Claus process has emerged. In the super-Claus process, the sulfur recovery can reach up to 99% and 99.5%, respectively, after adding a selective oxidation step or a hydrogenation reactor followed by a selective oxidation reactor on the basis of Claus. For the purpose of meeting the atmospheric emission standard, acidic gas in the outlet of reactor should be combusted at 1,200°C to transform the remaining H2S into SO2. 

Hydrogen explosions in units 1, 2 and 4 and pressure venting operations in the reactor vessels caused massive releases of radioactive material to the atmosphere and environment. The prevailing winds transported most of the atmospheric emissions in an easterly direction into the Pacific Ocean region. On the 8 stage International Nuclear Event Scale (INES) the accident was rated as 7, the highest rating on this scale. ... 

When the mercury present in the atmosphere is primarily in the form of an organic mercury compound, it may be preferable to utilise an aqueous scmbber. This method is particularly useful for control of emissions from reactors and from dryers. For efficient and economical operation, an aqueous solution of caustic soda, sodium hypochlorite, or sodium sulfide is reckculated through the scmbber until the solution is saturated with the mercury compound. 

Ammonium Phosphates. In the manufacture of ammonium phosphates, an atmosphere of ammonia may need to be maintained because the partial pressure of ammonia rises rapidly as either the temperature or the NH2/P20 mole ratio of the reaction mass increases. Phosphoric acid reacts quickly with ammonia vapor and is used in multistage reactor systems as a scmbber fluid to prevent NH emissions and recover ammonia values. For example, H PO scmbbing of coke-oven off-gases produces ammonium phosphates of relatively good purity. 

With the ever increasing awareness of the need of environment protection, the emission of solvent vapors and organic fumes into the atmosphere should be prevented by treating the exhaust through a proper scmbber. The solvent used for cleaning the reactor is usually consumed as part of the thinning solvent. Aqueous effluent should be properly treated before discharge. 

There is some question as to whether the total reactor contents will be discharged as assumed. If the reaction is in progress, then material already will have polymerized and will most probably not vent to the atmosphere, thus resulting in a significantly smaller emission. 

The ammonia is either injected as pure ammonia under pressure or in an aqueous solution at atmospheric pressure. Instead of ammonia, urea can also be used. The challenge of the process is to efficiently remove as much NOx as possible at full conversion of the reductant, as emission of NH3 from the SCR reactor would of course be highly undesirable. 

Direct acidihcation of cyanide waste streams was once a relatively common treatment. Cyanide is acidified in a sealed reactor that is vented to the atmosphere through an air emission control system. Cyanide is converted to gaseous hydrogen cyanide, treated, vented, and dispersed. 

Before the syngas from WGS reactor is separated into its primary components, the sulphur compounds, mainly in COS and H2S form, are removed to avoid its emission to the atmosphere. Sulphur is then recovered in either as solid in a Claus plant or as sulphuric acid. 

The characteristics of this kind of CL emission, design of reactors, CL reactions in gas phase, and applications as detection technique in gas chromatography (GC) and atmospheric research are extensively described in Chapter 13. 

A process is described [224] in which an exothermic reaction takes place in a semi-batch reactor at elevated temperatures and under pressure. The solid and liquid raw materials are both toxic and flammable. Spontaneous ignition is possible when the reaction mass is exposed to air. Therefore, the system must be totally enclosed and confined in order to contain safely any emissions arising from the loss of reactor control, and to prevent secondary combustion reactions upon discharge of the materials to the atmosphere. Further, procedures and equipment are necessary for the safe collection and disposal of solid, liquid, and gaseous emission products. 

In the electrolysis plant of Akzo Nobel in Rotterdam a hypochlorite production unit is in operation. This unit has two functions handling chlorine-containing waste gases from the plant and production of hypochlorite. The reaction is carried out in a two-step apparatus in which a liquid jet-loop reactor and a packed column are in series. In this way chlorine is converted to hypochlorite and emissions of chlorine to the atmosphere are avoided. 

In a continuous reformer, some particulate and dust matter can be generated as the catalyst moves from reactor to reactor and is subject to attrition. However, due to catalyst design little attrition occurs, and the only outlet to the atmosphere is the regeneration vent, which is most often scrubbed with a caustic to prevent emission of hydrochloric acid (this also removes particulate matter). Emissions of carbon monoxide and hydrogen sulfide may occur during regeneration of catalyst. 

The gaseous products of reaction, along with the supercritical water, leave the reactor. In some processes, effluent is used to preheat the feed to operating temperature, either by a heat exchanger, or by recirculating part of it towards the reactor. The remaining effluent is cooled and taken as emission at atmospheric pressure. 

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