CPC Corporation finds low maintenance solution for reliable SRU offgas cleaning
Refineries worldwide are subject to a variety of ever more stringent environmental laws that regulate their emissions. For many that plethora of rules often make it a struggle to combine the twin goals of compliance and cost control. Reliability and efficiency of Sulphur Recovery Units (SRUs) and its Tail Gas Treatment process is key to meeting emission targets, minimising maintenance requirements and operator time so that refiners are free to focus their attention on their core business. Finding the system that achieves this is easier said than done though, particularly when emission levels and investment budget are both low.
In the past, a common solution to improving reliability has been to install a highly efficient amine-based Tail Gas Treatment Unit (TGTU) downstream of the Claus plant. But why set out to kill a mosquito with a bazooka? CPC, a large Taiwanese state-owned refining corporation, chose a more efficient and cost-effective option, combining a slightly less efficient TGT process with the highly flexible MECS® DynaWave® reverse jet scrubbing technology (licensed by DuPont Clean Technologies). This allows the refinery to remove sulphur efficiently on a small plot space at lower capital expenditure while at the same time obtaining high on-stream time.
Meeting stringent emission targets at the CPC Ta-Lin refinery
The CPC Ta-Lin Refinery with a 300,000 bpsd capacity is set to rise its capacity to 350,000 bpsd as the older Kaohsiung refinery was closed a couple of years ago due to environmental reasons. At the Ta-Lin refinery, gasoline and diesel are the main products. This refinery operates one 2-stage and three 3-stage sulphur recovery units. The combined capacity of those Claus units is 780MTPD. In order for CPC to meet Taiwanese government air emission regulations at the Ta-Lin refinery, the DynaWave® reverse jet scrubbing technology was installed at one of the SRUs, to guarantee reliable SO2 removal from the SRU off gas stream at all times. This system has now been in operation for about 3 years.
CPC, at that time, chose to combine a well-known sulphur recovery tail gas technology with the DynaWave® technology for its two-stage, two-train SRU ♯10 as the best process to reduce SOx and Total Suspended Particulate (TSP) emissions. Their DynaWave® scrubbers provide a very high SO2 removal efficiency (99.7%) and are very easy to operate.
For the Ta-Lin refinery SRU #10, every sulphur train is equipped with a DynaWave® system. Each system has two reverse jet stages in the inlet barrel, combined with a packing section inside the vessels. This set-up allows the scrubber to operate with an extremely high liquid to gas ratio, which makes it possible to bypass the upstream main tail gas treatment unit during SSM (Start up, Shut down and Malfunctioning) conditions. In addition, CPC installed high-efficiency diffusion bed mist eliminators in the vessels to reduce SO3 emissions.
To meet the requirements at CPC, DuPont Clean Technologies specifically designed the DynaWave® wet gas scrubbers to reduce SO2 levels ≤30 ppmv on a dry basis and SO3 levels to ≤30 ppmv on a wet basis, both values corrected to 6 per cent oxygen. Each of the two MECS® DynaWave® custom engineered scrubbing systems installed at Ta-Lin SRU #10, removes SO2 and SO3 from the gas stream based on the specific design inlet conditions.
This straightforward DynaWave® technology had allowed CPC to opt for an oxygen-enriched Tail Gas Treatment process, which runs under normal conditions. At the same time, it has offered them the added reliability of operating the Claus plant without interruptions during maintenance/malfunction of the main tail gas treatment process and still meet the imposed SO2 emission limits. The innovative set-up of a combined cost-effective Tail Gas Treatment process technology with the highly flexible and reliable DynaWave® technology has resulted in a smaller overall footprint, very simple operation, low maintenance as well as significantly lower capital investment at the start of the project (TIC).
Advantages of new scrubber to CPC Ta-Lin
Overall, CPC’s Ta-Lin refinery noticed a significant difference after installation of the DynaWave® reverse jet scrubbers in 2014. The sulphurous emissions from the SRU are now below environmental regulation limits at any given time, 24 hours a day, 365 days a year in both train ♯1 and ♯2.
Before installation of DynaWave® technology at SRU#10, the SO2 concentration at the stack was normally about 1,000 ppm. During the performance test of the DynaWave® scrubbers, which are installed downstream of each train of a two-stage Claus unit and a main Tail Gas Treatment process, the SO2 concentration detected from the stack was 9.15 and 0.23 ppm respectively.
In the meanwhile, the CPC refinery has also operated the DynaWave® scrubber system in the SRU bypass mode several times and says it believes the inlet SO2 concentration may have been up to 7000~8000 ppm. Even in that mode, CPC measured outlet SO2 gas below 10 ppm.
What is also particularly noticeable to CPC is how simple the scrubber system is to operate and the limited amount of maintenance it requires. The refinery estimates that the DynaWave® technology has allowed them to save at least 30 per cent of its overall TIC budget compared to the installation cost of an amine-based TGTU alone. The capital cost of the combined Tail Gas Treatment/DynaWave® process was less than 70 per cent of the estimated capital cost of a similar sized amine-based TGTU process alone would have been, in part because fewer pieces of equipment are required.
Taoyuan refinery solves environmental issues with DynaWave®
In July 2017, the CPC Taoyuan refinery started up a new DynaWave® wet gas scrubbing system to comply to stricter SO2 emission regulations from Claus tailgases. This other CPC refinery in Taoyuan began operating in 1976 and has a capacity of 200,000 bpd. Up to a few months ago, the refinery used to require seven to eight days after turnaround of the SRUs at the refinery before acid gas could be fed to the units and commence normal operation. As a result, off-gas from the catalyst would be released directly to the stack and into the air, causing environmental issues. CPC researched different solutions to resolve these issues, and eventually selected the MECS® DynaWave® scrubber also for this site.
“CPC chose the DynaWave® scrubber for the high reliability of its outlet gas emissions when inlet gas SO2 concentration varies,” explains William Lam, Senior Business Development Manager, Taiwan and Japan, “This means, there is no need to adjust DynaWave® equipment such as valves or pumps in order to meet strict emission targets. The SO2 removal efficiency of DynaWave® turns an average of 10,000 ppmv SO2 at the inlet into a guaranteed outlet of less than 50 ppmv SO2.” At start-up, this summer, CPC technical teams measured only 10 ppmv SO2 at the stack outlet.
“The tailgas of two 2-stage Claus units (SRU2 and SRU3) at the Taoyuan refinery are treated directly in one single DynaWave® scrubber with two reverse jet stages,” says Mr Lam. The SRUs have a capacity of 100 tons/day (SRU2) and 200 tons/day (SRU3), respectively.
DynaWave® technical performance details
The DynaWave® reverse jet scrubbing system is illustrated in Figure 1. It is a unique open bore, reverse jet scrubber that uses froth zone technology to achieve desulphurization in a wet gas environment. For SRU applications, the DynaWave® systems are installed after the incinerator to treat the SO2 before the outlet gas leaves through the stack.
The heart of this system is the reverse jet nozzle, a gas-to-liquid contactor that creates a zone of intense mixing. The feed gas enters the top of a vertical duct and collides with the scrubbing liquid that is injected upward through a large bore injector or reverse jet nozzle.
The reverse jet nozzle is a very large bore, open throat nozzle, fabricated of silicon carbide for corrosion and temperature resistance (see Figure 2) that creates the full cone liquid flow essential to producing a froth zone. The froth zone, a standing wave of highly turbulent flow, is produced at the point where the liquid is reversed by the gas. This froth zone creates a very high rate of liquid surface renewal and efficiently quenches the gas to the adiabatic saturation temperature. At the same time, it converts all the SO3 present to acid (H2SO4) mist and absorbs the SO2.
The DynaWave® reverse jet scrubber can be designed to quench hot gases up to 1200°C. In addition to quenching and acid gas absorption, it can also efficiently remove particulate. This feature offers an extra reliability benefit in case elemental sulphur particulates enter the system.
CPC has installed several DynaWave® scrubbers over the last 10 years to treat different refinery off-gas streams and is so convinced of its benefits that the company is planning on installing DynaWave® scrubber technology at the next available opportunity for other SRU plants in the company’s refining complexes.
The authors are grateful to Mr. Jinn-Kuen Lu, head of the technical service sub-section and Mr. Wei-Chen Ke, No.10 SRU Superintendent at the Ta-Lin refinery of CPC Corporation, Taiwan for their support in the preparation of this case study.
In a box:
DynaWave® reverse jet benefits to CPC’s Ta-Lin refinery SRU
• Bypass of the upstream Tail Gas Treatment process while still meeting the required sulphur removal efficiency
• Guaranteed overall DynaWave® system sulphur removal of 99.7%
• Guaranteed SO3 emissions reduction
• Simple operation, low maintenance and little operator attention required
• Allows for significant capital cost savings in the main Tail Gas Treatment process selection with less equipment, smaller footprint and significantly less complexity than a typical amine based TGTU set-up.
• Higher on-stream reliability than a typical amine based TGTU alone, as DynaWave® technology provides a back-up function when the main Tail Gas Treatment process fails.
DynaWave® reverse jet benefits to CPC’s Taoyuan refinery SRU
• Compact and simple system that can be fitted into the existing plants with very limited space available.
• Important capital cost savings as no other tail gas treatment process installed upstream of the DynaWave® unit.
• Simple operation, low maintenance and little operator attention required
• High on-stream reliability
• Guaranteed low SO2 levels at stack.
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About DuPont Clean Technologies
DuPont Clean Technologies applies real-world experience, history of innovation, problem-solving success and strong brands to help organizations operate safely and with the highest level of performance, reliability, energy efficiency and environmental integrity. The Clean Technologies portfolio includes STRATCO® alkylation technology for production of clean, high-octane gasoline; IsoTherming® hydroprocessing technology for desulfurization of motor fuels; MECS® sulfuric acid production and regeneration technologies; BELCO® air quality control systems for FCC flue gas scrubbing and other refinery scrubbing applications; MECS® DynaWave® technology for sulfur recovery tail gas-treating solutions; and a comprehensive suite of aftermarket service and solutions offerings. Learn more about DuPont Clean Technologies at http://www.cleantechnologies.dupont.com.
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