The Heat Is On! – Why Temperature Plays an Important Role in Sulfur Recovery

The iconic skyline of Alberta’s natural gas sector is marked by labyrinthine tubes and tunnels, pipes and platforms. Atop it all—like candles on the cakes of carbon—are sputters of live flame, alighting the morning sky.

Far more than just a deterrent to low-flying aircrafts (and birds), the powerful heat of the reaction furnace ensures sulfur extraction is maximized, and the purity of outflow is an optimal makeup for cleanliness and machine reliability.

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Too Hot to Handle:

Working with sour water means bringing all the good along with the bad. Side reactions inside the reaction furnace will invariably produce unwanted products like CO, H2, COS, and CS2. Luckily, other contaminants such as BTEX, Mercaptans, NH3, HCN, Methanol, and HCs may be destroyed in the reaction furnace with proper calibration and sufficient heat.

While 900℃ (1650℉) is the minimum temperature for flame stability, heats of 1050℃ (1920℉) or above are capable of destroying the unwanted contaminants. Bear in mind the reaction furnace is kinetically limited based on residence time, turbulence, and temperature, as well as burner efficiency.

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Through the Fire and Flames:

In our Sulfur Recovery experience, combustion air flow rates are nearly always off by at least 10–20%. While this is standard, we must work to ensure this margin of possible error is not exacerbated. Proper mixture of gasses and the installation of a high-efficiency burner can increase reaction furnace temperatures up to 100℃, which helps to reach the target temperatures mentioned previously.

This is crucial not only for efficiency, but for optimal refinery health. Proper burn-off of ammonia in the reaction furnace is essential, as residuals can carry over to the condensers and converters, bringing with them the risk of forming ammonia salts. These salts will negatively impact heat transfer and recovery efficiency. As with most sulfur recovery unit issues, you won’t know there is a problem until it is too late.

As with any efficient furnace system, management of both inflow and output should be carefully monitored, with changes to procedure made according to the changes in both. Ensure your plant is optimized for the feed it receives. For example, when H2S qualities are low in gas plants, a front side split configuration is often best for ensuring minimal additions of air and nitrogen to the system.

Conclusion:

Sulfur recovery isn’t always easy, but it is undoubtedly important. In the end, you should run your reaction furnace like you would your bathtub: the hotter, the better; the better, the cleaner! Learn more about how we can help you optimize your Sulfur Recovery by contacting us at our website, subscribing to our newsletter, or by giving us a call today.

Ammonia Analysis – SRU Protection

SRE is the only firm in the Oil & Gas industry that can provide timely, on-site results with respect to ‘bulk’ and ‘trace’ ammonia testing. In addition to our standard ‘bulk’ ammonia analysis of refinery-based sour water stripper (SWS) acid gas feed streams, we are capable of measuring the ammonia content (i.e. ppm level) in amine acid gas and the stream exiting your reaction furnace (RF). These specialized services are another example of SRE’s commitment to the efficient and long-term operation of our clients’ SRUs by way of research and development.

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Based on 20+ years of field-testing experience, SRE strongly recommends ammonia breakthrough from the RF is kept below 150 ppm. The prevention of ammonia salt formation in downstream condensers will ensure optimal sulfur recoveries are realized without capacity reduction, all while preventing costly shutdowns to unplug or replace condenser tubes.  While on-site, SRE Engineers will work with operations to maximize ammonia destruction by way of optimizing your front-side split parameters and, if applicable, adjusting the fuel gas co-firing strategy.

The combination of an SRU performance test and ammonia destruction study will minimize the potential risk of downstream ammonia salt formation in your SRU. SRE’s specialized services are designed to protect your facilities, personnel, and bottom line.

Breakdown: Claus Processing Units

Today we will be breaking down the different components of Claus Processing Units. Let’s take a look at each component and some best practices to guide you as you consider your own operations.

Reaction Furnace

This is the first unit in the Sulfur Recovery Unit (SRU) process where feed enters and where thermal combustion happens. Most of the heat is produced in this section due to the highly exothermic reaction (H2S is burned using oxygen to produce desired amount of SO2). The inner walls of the reaction furnace are lined with refractory bricks to protect the shell of the vessel from the extreme heat.

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Wasteheat Boilers

The wasteheat boiler is attached to the back of the reaction furnace. This is where most of the heat removal takes place. These boilers are available in either a one-pass or two-pass design. A two-pass is used when there is a hot gas bypass already in place. By sending hot, processed gas to the first converter, the tube sheet is protected from high temperatures and sulphite attacks. When it comes to removing heat, the waste heat boiler is your friend— just let that hot steam rise to the top!

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Claus Process Condenser

The Claus process condenser is an excellent shell and tube heat exchanger. Its function is to remove sulfur and heat. It separates gas and the liquid leads into your liquid-sulfur run downs. It maintains an outwards temperature in the range of 150°C to 165°C to minimize the sulfur vapour carry-over to the incinerator. Any higher than that and things might get frenetic! Keep in mind that condensers achieve low pressure steam production — 50 psig. Use this steam in heat tracing, as desired. That steam is produced on the shell side, with sulfur product on the tube side.

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Reheater

Reheaters play a crucial role in maintaining sulfur temperature and avoiding condensation in the converters. Remember that processed gas leaves the condenser at the sulfur dew point temperature. This temperature must be increased. This increase provides optimal temperature for the Claus reaction in the gas phase and on to the converters.

Although two reheating methods exist, one is clearly superior. The direct reheating method is less desirable, as it adds additional sulfur bearing compounds to the process; this immediately lowers the overall practicable efficiency of the SRU. Moreover, between 0.1-0.5 % loss of sulfur can occur through this method.

Indirect heating is preferred for this reason. Harnessing the mighty power of steam, no added compounds can crawl through the pipes and into your end product. Simple to control and with no effect on overall practicable efficiency, indirect heating is the industry gold standard. Cost issues may arise, however, as some refineries see steam costing up to $5 per ton. The key point here is to focus on maintaining a 2:1 H2S to SO2 ratio.

Whatever the method, once converted and reheated the sulfur moves to the catalytic converter stage and incineration stage.

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Catalytic Converter , Thermal Incinerators and Instrumentation

The catalytic reaction occurs at this stage. Through an exothermic reaction, heat is released, and the temperature begins to rise in the catalyst bed. Temperature control, as always, remains critical. Here, Claus reaction is favoured at lower temperatures. We want the processed gas to be in the gas phase.

Once catalyzed the thermal incinerator comes into play by converting the remaining off gas into SO2. The temperature of your incinerator should not exceed 650°C. Keep in mind that this is controlled by the amount of fuel gas and air being burned. Be sure to monitor SO2 concentrations at ground level for proper plume dispersion. Instrumentation can help monitor oxygen levels within a 2-4% range, but they are not always accurate. Make sure you understand the normal base conditions to avoid excess temperatures and any accidents.

We hope this blog was informative to you and your Claus Processing Unit aspirations. Follow our blog for more pertinent and useful updates in the field of sulfur recovery.