HTS & LTS PSV vent

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aashish1220
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HTS & LTS PSV vent

Post by aashish1220 »

Why the HTS and LTS PSV vent open to open atmosphere, where methanator PSV vent and reactor top vent is connected to flare system. Are there PSV vent can connected to Flare system to prevent the exposure to open environment.
bedmonds
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Re: HTS & LTS PSV vent

Post by bedmonds »

Hi, Not sure of the details of the subject plant but a thought is that ammonia venting is best flared to destroy the ammonia, HTS and LTS gases are high is CO2 so if sent to the same flare there is a real risk of blockage with ammonimum carbonate or carbamate. A counter example is plants by Uhde which use a common flare for all gases without to much difficulty but the risk remains depending what sources are leaking into the flare stack at low flows so the flare stack not being hot.
aashish1220
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Re: HTS & LTS PSV vent

Post by aashish1220 »

Thanks bedmonds
This case is related to Haldor topsoe plant and common flare is also dedicated for all types of gas release.
rajneesh_jauhari
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Re: HTS & LTS PSV vent

Post by rajneesh_jauhari »

Dear Aashish
All vents (including HTS/LTS) should be connected to Flare and not to open atmosphere.
Yes, you can lay two different types of flare header up to the same Flare Stack with adequate internal design. One vent header for process gas from front end and other one for vent gases from back end of ammonia plant.
Please note that there is a risk if gas is venting to atmosphere.
naseemce
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Re: HTS & LTS PSV vent

Post by naseemce »

connection of HTS and LTS PSV vents with flare is depends on material of construction because of CO2 in gases and steam . Also its connection with the backend PSV vents is also concern due to ammonia and CO2 which will lead to form highly corrosive carbamate compound so usually FE and BE vents are separate and CO2 removal separate however surely BE to flare.
astromo
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Re: HTS & LTS PSV vent

Post by astromo »

A number of ammonia plants dating back to the 60s and 70s, that are still operating, were designed with vents rather than flares for PSV relief disposal.

Carbamate formation due to NH3+CO2 reaction can block vent headers and compromise relief discharge rate. I would place this factor as the key concern for avoiding combination of the two species above corrosion potential.

Vents were commonly used decades ago instead of flares because (amongst other factors) they are - cheap to build and operate, greenhouse gas emissions were of little concern and the potential for toxic gas release was less concerning to the local community.

Arguably, flares represent "best" practice and (in my opinion) should be considered as the baseline approach for hazardous gas disposal for new designs.
Last edited by astromo on Thu Oct 01, 2020 8:52 am, edited 1 time in total.
vpattabathula
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Re: HTS & LTS PSV vent

Post by vpattabathula »

In modern day NH3 plant design, all process vents should be connected to flare headers. Its considered as a best practice to have separate flares for process gas (typically front-end) and NH3 (back-end).
astromo
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Re: HTS & LTS PSV vent

Post by astromo »

vpattabathula wrote: Mon Sep 28, 2020 10:30 pm In modern day NH3 plant design, all process vents should be connected to flare headers. Its considered as a best practice to have separate flares for process gas (typically front-end) and NH3 (back-end).
To pick up on this point, the importance of backpressure on relief design (especially conventional PSVs) is another reason for separating front end relief systems from the back end given the system design pressure difference between the two parts of the plant.
hppandya1234
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Re: HTS & LTS PSV vent

Post by hppandya1234 »

In old design of ammonia plants built in sixties were having two PSV for flaring hydrogen bearing gas to atmosphere rather than to dedicated flares. In few cases steam connection was provided to vent headers. Both had separate vent headers and there were few incidence of fire in vent header at methanator outlet. This was not a safe design and operation. All new plants have PSVs connected to flare stack.
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