Hot gas bypass

Another pressure control method is a hot gas bypass. The author has seen a retrofitted hot gas bypass system solve an unsatisfactory pressure control scheme. In the faulty system, a pressure control valve was placed between the overhead condenser and the lower reflux drum. This produced en atic reflux drum pressures. A pressure safety valve (psv) vented the reflux drum to the flare to protect against over-pressure. A psv saver control valve, set slightly below the psv relieving... 

The fix for the erratic reflux drum pressure problem was to provide for separate pressure control of the fractionator column and the reflux drum. A new pressure control valve was installed upstream of the condenser and the old condenser outlet control valve was removed. A hot gas bypass, designed for 20% vapor flow, was installed around the pressure control valve and condenser. A control valve was installed in the hot gas bypass line. The column pressure was then maintained by throttling the new control valve upstream of the condenser. The reflux drum pressure w as controlled by the hot gas bypass control valve and the psv saver working in split range. The new system is shown in the figure below. 

Chin states that a scheme having only a control valve in the hot gas bypass line manipulated by the column... 

For a total condenser, accumulator level is typically set by varying distillate draw. For a partial condenser, it can be controlled with a condenser hot gas bypass. 

Hot gas bypass valve, to keep the evaporating temperature up above freezing point. 

There are several methods of reheating the vapor, including hot gas exchange, in-line burners, hot gas bypass, or indirect steam reheat. Each has advantages and disadvantages generally indirect steam reheat is most expensive but yields higher recoveries. 

Figure 20.11 is a sketch of a once-through Claus process using a hot gas bypass for reheat. Sufficient air is used to bum one-third of the H2S and all hydrocarbons. Steam... 

HOT DECK - The heating section of a multizone system. HOT GAS BYPASS - Piping system in refrigerating unit which moves hot refrigerant gas from condenser into low-pressure side. 

The flow sheet of a Standard Claus unit is shown in Fig. 5.10. Essentially, such a unit consists of the combustion chamber section with a waste heat boiler and two reactors. Such plants are normally used for sour gases containing more than some 45 vol. % of H2S. The sour gas is fed to the combustion chamber together with air or, if required, with fuel gas it is already in this combustion chamber that as much as 70% of the hydrogen sulfide are reacted to elemental sulfur. The gas mixture leaving the combustion chamber is cooled down in a waste heat boiler to the inlet temperature required for the first catalytic stage. The temperature is controlled by what has been termed a hot gas bypass. 

Figure 12.44 Hot gas bypass with condenser below drum...

Figure 16.16 is a sketch of a once-through Claus process using a hot gas bypass for reheat. Sufficient air is used to burn one-third of the H2S and all hydrocarbons. Steam usually is generated in the waste heat boiler, where the combustion products are cooled, and sulfur is condensed. The gas must be heated before introduction to the reactor to prevent sulfur condensation in the reactor... 

---