Acid Gas Absorber Side-Stream Chiller for Height Reduction
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Solution Overview
Problem
Existing acid gas removal processes face high capital and operating costs due to the need for large hydrogen sulfide absorber columns, which are exacerbated by the residence time requirements for preventing pump dry-running and the heat associated with carbon dioxide absorption exotherms.
Innovation Solution
The process involves a sour gas stream being sent to a first absorber with a side-stream withdrawal, passing through a holding tank and chiller before return, and the overhead stream being sent to a pump-around circuit for a second absorber, allowing for efficient use of the hydrogen sulfide absorber without increasing its size by utilizing a chiller to remove heat from the carbon dioxide absorption exotherm and providing additional contact stages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the absorber column height is increased to meet residence time requirements for preventing pump dry-running, then pump reliability is improved, but capital cost increases
Solution Approach 1:
The absorber column is segmented into multiple functional sections with a liquid trap-out tray creating distinct zones. The side draw is positioned at a specific elevation to provide sufficient liquid head for the pump while maintaining compact overall column height. This segmentation allows the system to meet residence time requirements without proportionally increasing total column height.
Solution Approach 2:
Instead of solely increasing vertical height to provide residence time, the invention uses a horizontal side draw arrangement with a liquid trap-out tray that creates a lateral liquid collection zone. This dimensional approach provides the necessary liquid inventory for pump operation without linearly increasing the absorber column height.
2Loss of energy
If solvent circulation rate is reduced through chilling, then operating cost decreases, but absorber column height must increase to maintain residence time
Solution Approach 1:
The solvent stream is chilled in advance in a separate heat exchanger before being reintroduced to the absorber column. This preliminary cooling action removes the exothermic heat of absorption without requiring additional column height, as the cooling occurs in an external circuit rather than within the absorber itself.
Solution Approach 2:
The absorption process is segmented into multiple stages with intermediate cooling. The side draw stream is separated and chilled independently, then returned to the absorber. This segmentation allows heat removal without increasing the main absorber column height, enabling reduced solvent circulation rates while maintaining compact equipment dimensions.
3Use of energy by stationary object
If a side draw is chilled to reduce solvent circulation rate, then utility cost decreases, but absorber capital cost increases due to height requirements
Solution Approach 1:
The solvent is pre-cooled in an external heat exchanger before entering the absorber column. This preliminary action removes the exothermic heat of absorption in a separate unit, allowing the use of smaller, more economical absorber columns while still achieving the desired solvent circulation rate reduction through chilling.
Solution Approach 2:
The cooling function is moved from the vertical dimension (increasing absorber height) to an external horizontal dimension (separate heat exchanger and side draw system). This dimensional shift allows utility cost savings from chilling to be achieved without the corresponding increase in absorber capital cost that would result from increasing column height.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces the height requirements of the absorber by up to one-third, prevents pump dry-running, and economically justifies chilling by providing additional contact stages, thereby enhancing the efficiency and reducing capital costs.
Implementation Method 1
a side-stream chiller before returning the side-stream to the absorber
Implementation Method 2
remove the heat associated with the carbon dioxide absorption exotherm
Implementation Method 3
a pump-around chiller before providing a slipstream to the first absorber
Implementation Method 4
treated with a solvent in at least one absorber to selectively remove one or more sulfur compounds, such as a hydrogen sulfide or a carbonyl sulfide, and carbon dioxide
Data Source
AI summary
One exemplary embodiment can be a process for increasing an efficiency of an acid gas removal zone. The process can include sending a sour gas stream including at least one gas to a first absorber providing an overhead stream absorbing the at least one gas; withdrawing a side-stream from the first absorber and passing the side-stream through a holding tank, a side-stream fluid transfer device, and a side-stream chiller before returning the side-stream to the absorber; and passing the first absorber overhead stream to a pump-around circuit for a second absorber. Usually, the pump-around circuit may include a flash drum, a pump-around fluid transfer device and a pump-around chiller before providing a slipstream to the first absorber and another portion to the second absorber.