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A process and apparatus for removing SO2 from a gas stream having the steps of scrubbing the SO2 with an ammonia scrubbing solution and removing any aerosols generated by the scrubbing in a wet electrostatic precipitator. The scrubbing solution is maintained at a pH between 6 and 8 to increase the speed of absorption of SO2, to Increase the ratio of sulfite to bisulfite which also facilitates the oxidation of SO2, and to avoid the need to use exotic, corrosion resistant alloys. Ammonium sulfate, a valuable fertilizer, can be withdrawn from the scrubbing solution.
Fossil fuels are burned in many industrial processes. Electric power producers, for example, burn large quantities of coal, oil, and natural gas. Sulfur dioxide (“SO2”) is one of the unwanted byproducts of burning any type of fossil fuel. It is known to cause acid rain, and to have serious negative health effects on people, animals, and plants. A great deal of research has been done to find a way to economically remove SO2 from flue gas streams before it enters the atmosphere.
The pH of the ammonium sulfate solution should be kept between about four and six. This range is the result of a compromise between competing factors. On one hand, ammonium sulfate solution is capable of absorbing SO2 more rapidly when its pH is higher. The ability to absorb SO2 better implies that the size of the scrubbing tower can be smaller, thus saving capital costs. In addition, the liquid to gas (“L/G”) ratio can be smaller, meaning less liquid will be required and operating costs will be lower.
On the other hand, higher pH levels are also associated with the release of free ammonia from solution, often termed “ammonia slip.” In addition to incurring an economic loss because of lost ammonia, free ammonia in the scrubbed flue gas reacts with uncaptured sulfur dioxide and trioxide to create an ammonium sulfate/bisulfite aerosol that is visible as a blue or white plume in the stack discharge, leading to secondary pollution problems. Controlling the amount of free ammonia in the desulfurization process is in part a function of the ammonia vapor pressure, which results from a combination of pH and levels of unoxidized ammonium sulfite that remain in the absence of sufficient oxygen. Therefore, high pH values and high levels of unoxidized ammonium sulfite promote ammonia slip.
Measurement System
Process Liquid Analyzer:
Features
Features
Sensor Selection:
SC25 sensor from Yokogawa is the perfect sensor for this application. High temperature sensor SC25 because of its design can serve purpose.
Features SC25V
Cable:
Retractable fitting:
On-line measurements always present extra challenges compared to at-line measurements, for example, when maintenance needs to be done. Applications like this where the sensors have to be removed without interruptions or shut-downs the PR10 is especially suitable. Without any special tools the PR10 can be retracted safely from the process up to 5 bar.
For ease of use optional flush ports are available. In the retracted position the sensor can be kept moist, cleaned or even calibrated. This can all be done without process interruption or disassembly of the armature.
Better life of sensor, improve end product quality.
Note: For additional information on this application contact the local Yokogawa Process Liquid Analyzer Department
The SC25F is a digital smart pH sensor in a 12 mm design that includes an integral temperature element and a Liquid earth electrode.
The SC25V is a pH sensor in a 12 mm design that includes an integral temperature element and a Liquid earth electrode.
The model FLEXA® two-wire analyzer is used for continuous on-line measurements in industrial installations. It offers an option for single or dual sensor measurement, making it the most flexible 2-wire analyzer available. The model FLEXA® modular designed series analyzer offers 4 parameter choices – pH/ORP (oxidation-reduction potential), contacting conductivity (SC), inductive conductivity (ISC) or dissolved oxygen (DO) – with the respective sensor module.
The new EXAxt 450 series builds on the superior functionality of the industry leading Yokogawa EXA series by enhancing the EXA's proven operation and application flexibility. The Model 450 series feature a uniquely simple touch screen menu structure that offers a choice of five different languages (English, French, German, Italian or Spanish).
pH and ORP meters, analyzers and transmitters are used for continuous process monitoring of pH and ORP to ensure water/product quality, monitor effluent discharge, batch neutralization, pulp stock, scrubbers, cooling towers, chemical, water/wastewater treatment and many other applications.
Contact a Yokogawa Expert to learn how we can help you solve your challenges.