On the emergency shutdown issue of vinyl chloride with hydrochloric acid desorption equipment
Thread Content
Dear sea friends, does your vinyl chloride come equipped with a hydrochloric acid desorption unit? In the water-alkali washing section, a new hydrochloric acid dehydration unit has been added. The concentrated acid is supplied to this dehydration unit from the combined tower; the hydrogen chloride gas produced is sent for mixing and dehydration, while the dilute acid returns to the combined tower. The pipeline carrying the concentrated hydrochloric acid to the dehydration unit is equipped with a control valve that is interlocked with the control valve of the acetylene inlet mixer in the mixing and dehydration process – if the acetylene valve is closed, this control valve also closes as a result of the interlock. A possible issue now is that the hydrochloric acid dehydration unit can be stopped first during normal shutdown. However, in the event of an emergency that requires an immediate shutdown, once the valves for hydrogen chloride and acetylene are closed, the valve for the concentrated acid in the separation unit shuts down as a result of interlocking. At this point, the evaporator in the separation unit stops receiving steam immediately, and a large amount of hydrogen chloride gas is generated. It may be necessary to use additional pipes to send this hydrogen chloride gas to other sections (since the mixing and dehydration process has already been shut down urgently). Also, in the hydrochloric acid desorption unit, the manufacturer states that the evaporator should be cooled slowly, and it is essential to wait until the evaporator reaches room temperature before stopping the supply of concentrated acid. Colleagues, how do you control the hydrochloric acid stripping unit and the emergency shutdown of vinyl chloride? I’d appreciate some advice!
The last edit to this post was made by clq20040107 on 2010-11-21 at 09:36. As far as I know, in the case of an emergency shutdown of the hydrochloric acid extraction unit, it is not the steam that is stopped immediately; instead, the acid supply is halted first, and then the steam supply is reduced gradually. As long as the acid feed is stopped, only a small amount of hydrogen chloride and water vapor will be generated in the rectification tower; after passing through the cooler, it essentially turns back into condensed acid, with no hydrogen chloride produced. Additionally, the hydrochloric acid dehydration unit is equipped with a small water absorption tower; the acid after absorption goes into the dilute acid tank. This tower is used to absorb unqualified hydrogen chloride gas at the start of operation. If not, then pipe it to a location with an absorption unit; this can be a combined absorption tower, or a small additional absorption tower can be installed within the existing unit.
Reply to 2# clq20040107: Yes, thank you for your answer. It seems necessary to add an additional pipeline from the hydrogen chloride outlet of the desorption unit to the combined tower (in the design, the desorption unit does not have an absorption device; it only has a cooler). When the control valve for the mixed-dehydrated acetylene is closed, the steam valve also closes as a result of interlocking. I wonder whether this interlocking control should be removed; my experience is limited, and I’m not sure what purpose it serves Moreover, the design unit for hydrochloric acid removal requires that the steam to the evaporator be turned off slowly, so that it can cool down gradually?
After the wastewater has been treated, a collection tank is added before it is sent to the synthesis wash tower; the wastewater is pumped into this synthesis wash tower using a pump. A pipeline is led from the outlet of the pump to the top of the collection tank, and a polypropylene injector is installed at the top of this tank. In case of an emergency, this injector absorbs the HCL present in the system. It is acceptable for diluted acid to enter the synthesis wash tower; this constitutes an emergency recovery system for the treatment process.
When the mixed-dehydrated acetylene control valve is closed, the steam valve will close in a coordinated manner; this interlock can be removed as long as it can be handled by the control room staff.