Ammonium Thiosulfate Tail Gas Treating for Sulfur Recovery
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Solution Overview
Problem
Current sulfur recovery processes in oil refineries and gas plants face challenges in efficiently recovering sulfur and nitrogen-containing compounds due to high energy consumption and limited capacity, with existing methods being intensive and costly, and struggling to manage variable sulfur and ammonia ratios in off-gas streams.
Innovation Solution
A continuous process utilizing ammonium thiosulfate solution as the primary absorption agent for high-efficiency absorption and recovery of sulfur and nitrogen components in incinerated Claus SRU off-gas streams, allowing for flexible control of ATS production and pH management, and enabling the use of additional ammonia to accommodate varying gas stream conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If SCOT-TGTU process is used for further treatment of Claus SRU off-gas, then sulfur recovery efficiency is improved, but energy consumption and process cost increase significantly
Solution Approach 1:
The patent changes the chemical parameters of the absorption process by using ammonium thiosulfate solution with controlled pH (6.5-8.0) and specific composition ratios. This allows efficient sulfur dioxide absorption without the high energy consumption of thermal reduction processes. The process operates at ambient or near-ambient temperatures, fundamentally changing the energy intensity parameter compared to conventional SCOT-TGTU thermal processes.
Solution Approach 2:
The patent introduces ammonium thiosulfate solution as an intermediary absorption medium between the sulfur dioxide-containing off-gas and the final sulfur product. This intermediary chemical system enables sulfur recovery through chemical absorption and precipitation rather than high-energy thermal reduction, resolving the contradiction between recovery efficiency and energy consumption.
2Productivity
If ammonium thiosulfate solution is used as absorption agent, then sulfur recovery efficiency is improved, but control of SO2:NH3 molar ratio becomes problematic due to variable upstream processes
Solution Approach 1:
The patent implements dynamic process control by continuously adjusting the ammonium thiosulfate solution composition and pH (maintained at 6.5-8.0) to accommodate variable incoming gas streams. The system can adapt to changing SO2 and ammonia concentrations from upstream processes, transforming a static stoichiometric limitation into a dynamic, controllable process parameter.
Solution Approach 2:
The patent employs feedback control mechanisms to monitor and adjust the absorption process in real-time. By continuously measuring gas stream composition and adjusting the ammonium thiosulfate solution properties accordingly, the system maintains optimal absorption efficiency despite variations in upstream process output, resolving the control difficulty associated with variable SO2:NH3 ratios.
3Adaptability or versatility
If additional ammonia is added to accommodate variable gas stream conditions, then adaptability is improved, but pH control and ATS production volume control become more complex
Solution Approach 1:
The patent systematically manages multiple chemical parameters (ammonia concentration, pH, temperature, solution composition) to achieve adaptability. By establishing interrelationships between these parameters—particularly maintaining pH within 6.5-8.0 while adjusting ammonia levels—the system achieves gas stream adaptability without excessive complexity. The parameter changes are coordinated rather than independent, reducing overall control complexity.
Solution Approach 2:
The ammonium thiosulfate solution serves multiple functions simultaneously: it absorbs sulfur dioxide, buffers pH, provides ammonia for sulfur recovery, and produces marketable ATS product. This multi-functionality reduces the need for separate control systems for each function, simplifying overall process complexity while maintaining adaptability to variable gas streams.
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 process maximizes sulfur recovery, reduces sulfur emissions, and increases the capacity of sulfur recovery units while producing a valuable ATS product that can be used as an agricultural fertilizer, accommodating a wide range of gas stream analyses and flow rates, and minimizing waste production.
Implementation Method 1
ATS solution is the primary absorber solution for high efficiency absorption, reaction and recovery of sulfur and nitrogen components in incinerated Claus SRU off-gas streams
Implementation Method 2
This sulfite-rich ATS mixture however, is not directly pH controlled with additional ammonia and not continuously re-circulated through the SO2 contactor with a separate re-circulating pump for maximum SO2 recovery efficiency
Data Source
AI summary
The present invention relates to a system and process utilizing ammonium thio sulfate solution (ATS) as the primary liquid absorption agent that is re-circulated through an SO2 Contactor/Absorber for high efficiency contacting and absorption of sulfur dioxide, SO2 from a combustion gas stream generated by incineration of a Claus Sulfur Recovery Unit (SRU) off gas stream (often referred to as a Claus tail gas stream) and also additional SO2 generated from incineration of additional sulfur containing streams. ATS is also re-circulated through a separate H2S Contactor/Absorber for absorption of and reaction with a Sour Water Stripper (SWS) off gas stream and additional H2S-Acid Gas (A.G.) streams to produce additional concentrated ATS. The process and equipment also provides the ability to readily switch between using ATS and ABS as the primary absorbent solution for SO2 absorption, depending upon the concentration of SO2 in the off gas feed streams.