Two questions regarding the PID diagram of the light hydrocarbon recovery unit
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While reviewing the PID diagram of the light hydrocarbon recovery unit, I encountered two questions; I would appreciate it if experts could help resolve them. 1. The diameter of the upward section of the pipeline that carries the overhead gas from the degasifier column to the reflux tank of the degasifier column changes from DN300 to DN250 to DN300. What is the purpose of installing these diameter-changing sections? 2. The on-site stop buttons for the deethanization reflux pump and the debutylization reflux pump are installed at a distance of 15 meters away from the pumps. What is the purpose of this distance requirement?
The second design intent should be safety, to enable the pump to be stopped safely in the event of a leak or fire!
Is the diameter change due to throttling? It’s not clear. The pump shutdown button is located 15 meters away from the pump; it should be an emergency shutdown button, not a normal shutdown button. When there is a material leak, people should not approach the area, and the pump should be stopped from a relatively safe distance
Is there a orifice flow meter or something at the section where the diameter changes? Secondly, since liquefied gas is flammable, explosive, and prone to leakage, these are the safety design requirements in place today
I didn’t see any attachments for insulating the pipeline
The purpose of reducing the pipe diameter is to increase the flow rate. The fluid exiting the cold box is in a gas-liquid two-phase state, and increasing the flow rate can prevent slug flow.
I agree with your view; I also think that narrowing the flow area is intended to increase the flow rate and prevent plug flow phenomena caused by the gas-liquid two-phase mixture. Another issue might be related to ensuring a safe distance – the design of firefighting water systems in some tank areas also deserves attention. Over the years, there have been many cases of secondary damage resulting from firefighting efforts: the fire wasn’t extinguished, but firefighters lost their lives and vehicles were damaged. If it were possible to deliver firefighting water from a distance, wouldn’t that make things safer?
President Gao, is there a control valve in the section where the diameter changes?
Is tower pressure control a critical control point?
Secondly, we can take a look at clause 7.2.15 of the Petrochemical Regulations
First, it is necessary to consider the specific location of the diameter change; its main function should be to increase the flow velocity； Second, many people upstairs say it is for safety reasons. I only have one question: if emergency shutdown is needed for safety, why not set it up in the DCS system?