Integrated Dry Nojso, Emissions Control System Sodium-based Dry Sorbent Injection Test Report

The DOE sponsored Integrated Dry NO&O, Emissions Control System program, is a Clean Coal Technology Ill demonstration, being conducted by Public Service Company of Colorado. The test site is Arapahoe Generating Station Unit 4, a 100 MWe, down-fired utility boiler burning a low sulfur Western coal. The project goal is to demonstrate up to 70 percent reductions in NO, and SO, emissions through the integration of: 1) down-fired IOWNO, burners with overfire air; 2) Selective Non-Catalytic Reduction (SNCR) for additional NO, removal; and 3) dry sorbent injection and duct humidification for SO, removal. This report documents the sixth phase of the test program, where the performance of dry sotbent injection with sodium compounds was evaluated as a SO, removal techniqus. Dry sorbent injection was performed “in-duct” downstream of the air heater (ahead of the fabric filter), as well as at a higher temperature location between the economizer and air heater. Two sodium compounds were evaluated during, this phase of testing: sodium sesquicarbonate and sodium bicarbonate. In-duct sodium injection with low levels of humidification was also investigated. This sixth test phase was primarily focused on a parametric investigation of sorbent type and feed rate, although boiler load and sorbent preparation parameters were also varied. The in-duct injection of sodium sesquicarbonate achieved the target 70 percent SO, emission reduction at normalized stoichiometric ratios ranging from approximately 1.6 to 2.2. (The stoichiometric ratio is 2 moles of sodium per mole of sulfur). The data exhibit day-to-day variations which were attributable to the sorbent feed system which utilized volumetric screw feeders. Sodium bicarbonate injection ahead of the fabric filter showed variable SO, removal characteristics which were attributed to the relatively low temperatures at the fabric filter inlet (i.e., on the order of 230 to 270°F). Injection of sodium bicarbonate at the air heater inlet, where the temperatures were on the order of 6OO”F, showed more consistent SO, removals. Under these conditions, sodium bicarbonate yielded a 70 percent SO, removal at a 2Na/S ratio of approximately 1 .l. ii FERCo-7037-R337 A byproduct of the scdiurn/SO, chemistry is the oxidation of NO to NO,, which may result in plume visibility. ‘The NO, production with sodium sesquicarbonate was less than with sodium bicarbonate. However, on some occasions, a faint visible plume was observed. The test program showed that NO, levels were not only dependent on the type and amount of sodium compound injected, but also on the fabric filter cleaning cycle. After each cleaning cycle, the NO, emissions increased markedly. A long-term test of nominally four months was conducted with sodium sesquicarbonate injection ahead of the fabric filter. A rolling average SO, removal of 40 percent was easily maintained for the duration of the test. Average NO, emissions during this test were 6.7 ppm and there were no occurrences of a brown plume at the stack. A four-week 70 percent removal test with sodium sesquicarbonate injection ahead of the fabric filter fell just short of the goal, with an average SO, removal of 67.9 percent. System availability during this test was only 94 percent primarily due to a 32-hour period when neither of the two sorbent injection systems were in service. The average NO, emissions during this test were 15.2 ppm, and a faint brown plume was visible on several occasions. . . III FERCo-7037-R337 ACKNOWLEDGEMENTS The authors would like to thank Mr. Jim Love, Arapahoe Plant Manager, and his maintenance and operating staff for the exceptional cooperation they have provided during this project. Special thanks are also deserved by Mr. Jerry L. Hebb, Mr. Tom Arrigoni, and Mr. Tim Mcllvried of PETC DOE, whose contributions are greatly apprecialed. We are all saddened by Tom Arrigoni’s and Tim Mcllvried’s deaths in the USAir accident. The advice and technical assistance provided by Mr. Jeff Stallings and Ms. Barbara Toole-O’Neil at EPRI have also been of great assistance throughout the project. Last, but definitely not least, is our appreciation to the many PSCo Engineering and Construction personnel and other contractors who have made the Integrated Dry NOJSO, Emissions Control System a success.