Hot process gases

In the DSN processes ammonia and air react over a platinum catalyst, and the process gas stream is cooled to the point where weak acid condensate is formed. Tail gases are also reheated by hot process gases and provide energy recovery in a gas expander. DSN processes differ from weak acid plants in that additional or different process steps are needed to achieve superazeotropic strengths of nitric acid100,104. 

The high temperature corrosion behaviour of different iron aluminides and iron-aluminium-chromium alloys containing 6-17 wt% aluminium, 2-10 wt% chromium and additions of mischmetal has been investigated in both air and hot process gases. 

A 25% oleum boiler—cheated either by steam or hot process gases. 

Many chemical industries have boilers for supply of steam— they are either fired by fuels like coal/oil or recover heat from hot process gases. It will be useful to familiarise aU plant operating persons with the important points for smooth and safe boiler operations. 

Reheat turbines The medium-pressure samrated steam from exit of a high-pressure steam turbine can be reheated by another source of hot process gases if available in the plant. More power can be generated by using this reheated steam through another mrbine. 

Captive power generators may be therefore installed in many chemical plants which are to be run by steam turbines. These can get the steam supply from coal-fired boilers or from waste heat recovery boilers operating on hot process gases. They can reduce dependence on supply of power from external grid. They... 

It can be generated by coal-fired boilers/or will be available from waste heat recovery boilers (WHRBs) which are heated by hot process gases, hot exit gases from the plant. 

Hot process gases which are to be cooled and are available in process plants. Flue gases after combustion of fuels. 

Typically, these units are installed in sulphuric acid plants and nitric acid plants to recover heat from hot process gases and thus produce steam. 

Another option for consideration is reheat turbines HP steam turbine can exhaust medium pressure saturated steam, which can be reheated by hot process gases if available and more power can be generated. 

It can be generated by the use of different fuels given above or by waste heat recovery boilers (WHRB) from hot process gases which need cooling as per process requirement. 

If HP steam is not available, then mechanical compressor can be used to suck and compress the vapour to a higher pressure and then reheat it to a higher temperature if a source of heat is available (say, hot process gases) in the plant. This can reuse the entire LP vapoitr from the evaporator if there is requirement in the plarrt. This can be possible in more instances, since this method does not increase the quantity of LP steam (but only increases its heating potential). 

Catacarb process An extraction process used to remove carbon dioxide from process gases by scrubbing the hot gases with potassium carbonate solution containing additives which increase the hydration rate of the gas in the solution. The Vetrocoke process is similar. See Benfield process. 

Flame or Partial Combustion Processes. In the combustion or flame processes, the necessary energy is imparted to the feedstock by the partial combustion of the hydrocarbon feed (one-stage process), or by the combustion of residual gas, or any other suitable fuel, and subsequent injection of the cracking stock into the hot combustion gases (two-stage process). A detailed discussion of the kinetics for the pyrolysis of methane for the production of acetylene by partial oxidation, and some conclusions as to reaction mechanism have been given (12). 

The CVD process is accomplished using either a hot-wall or a cold-wall reactor (Fig. 13). In the former, the whole chamber is heated and thus a large volume of processing gases is heated as well as the substrate. In the latter, the substrate or substrate fixture is heated, often by inductive heating. This heats the gas locally. 

The tubes that are around the flame get most of their heat energs t rom radiation. The tubes in the top of the chamber get their heat from com ec-tion as the hot exhaust gases rise up through the heater and heat ihc process fluid in the tubes. The principal classification of fired heaters relates to the orientation of the heating coil in the radiant section. The tube coils of vertical fired heaters are placed vertically along the walls of the combustion chamber. Firing also occurs vertically from the Hoor of the heater. All the tubes are subjected to radiant energy. 

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