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By Nathan Long Muskingum River Plant Emissions Reduction Programs.

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Presentation on theme: "By Nathan Long Muskingum River Plant Emissions Reduction Programs."— Presentation transcript:

1 by Nathan Long Muskingum River Plant Emissions Reduction Programs

2 2 Precipitators Ohio Environmental Protection Agency (EPA) dictates opacity must be below 20%. Other states may have different regulations. Units 1-4 Each unit has a Joy/Western precipitator. Consists of 16 fields powered by 8 transformer/rectifiers. Neundorfer voltage and rapper controls. Opacity averages between 5%-12% Unit 5 Research Cottrell – two boxes. Each box has 30 rectified fields. Neundorfer voltage and rapper controls Opacity averages approximately 5%.

3 3 Precipitator Problems Units 1-4 Casing leaks allows moisture to enter precipitator creating high levels of sparking thus driving power levels down. Transformer/rectifiers failing more frequently than in the past. Reaching end of life? Neundorfer controls aggresively ramp voltage back up following spark quenching which may be shortening life of transformer/rectifiers. Electrodes were failing causing grounds. Resolved by installing a heavier gauge electrode wire. Precipitators are undersized so any upsets often cause load curtailments to stay under 20% opacity. Unit 5 Precipitators are oversized. No real problems.

4 4 Sulfur Trioxide (SO3) and Ammonia (NH3) Flue Gas Conditioning System Used on units 1-4 (subcritical units) Decreases flyash resistivity to improve collection of ash in precipitators. Advantageous when sulfur content of coal drops below 3.5 lbs/Mbtu. SO3 system Molten sulfur stored in 100 ton tank (approx. 60 day capacity) at 143 deg. C (290 deg. F). Sulfur pumped through steam jacketed lines to sulfur burners. Sulfur gas passes through vanadium pentoxide catalyst which accelerates the natural process of the chemical reaction to ensure at least 95% of the sulfur dioxide is converted to sulfure trioxide. 15 kw (20 HP), 3600 rpm process air blower – 15 cm/min (530 scfm) 2.2 kw (3 HP), 3600 rpm purge blower keeps piping and nozzles clear when system is out of service. 6 injection probes distribute the SO3 into the duct upstream of precipitator.

5 5 Sulfur Trioxide (SO3) and Ammonia (NH3) Flue Gas Conditioning System NH3 System Used with SO3 system to enhance “collectibility” of the ash. Anhydrous ammonia stored as a pressurized liquid in a bulk storage tank. Tank equipped with 2 – 10 kw heaters which vaporizes the ammonia. Ammonia vapor passes through a regulating valve (1-5 ppm) before being injected through 6 probes.

6 6 Sulfur Trioxide (SO3) and Ammonia (NH3) Problems Sulfur Trioxide Must maintain proper insulation on steam jacketed sulfur lines or sulfur will solidfy. Experienced this on startups, had to heat lines with torches to get sulfur to flow. Improved insulation took care of the problem. The sulfur metering pumps are a submersible gear type pump with very close tolerances. The pumps wear and eventually will not pump at which time they have to be replaced and sent out for refurbishment. They cannot be repaired on site. When the system is shut down, the purge air blower must be in service or flue gas will come back into the lines and plug the probes. The probes are bulky and heavy and must be removed to be unplugged.

7 7 Sulfur Trioxide (SO3) and Ammonia (NH3) Problems Ammonia (NH3) Care must be taken not to over inject or it will foul the precipitator. Ammonia detection systems and alarms must be maintained around the storage tank and injection skids to alert personnel of any leaks.

8 8 Continuous Emissions Monitoring System (CEMS) All five units equipped with a redundant continuous emissions monitoring system. Monitors: Opacity Sulfur Dioxide (SO2) Nitrous Oxide (NOx) Carbon Dioxide (CO2) Flue gas sample is diluted with air 300:1 to extend life of instrumentation and make the system more reliable. Monitors analyze the gas sample and send raw data to a polling computer which calculates mass emissions rates. The CEMS technician performs daily checks of the data before sending on to AEP, Columbus. The data is submitted to the Ohio Environmental Protection Agency on a quarterly basis. Preventive maintenance is performed on the equipment on a quarterly basis. Monitors automatically calibrate daily.

9 9 Nox Reduction Goals Units 1- 2 Maintain NOx Emission Rate under 779 kg/kcal (0.44 lb/mbtu) Units 3-4 Maintain Nox Emission Rate under 466 kg/kcal (0.308 lb/mbtu) Unit 5 Maintain NOx Emission Rate under 101 kg/kcal (0.067 lb/mbtu) with SCR

10 10 Terminology n Theoretical air is the minimum air required for complete combustion of the fuel, resulting in stoichiometric combustion. n Stoichiometry (also called stoichiometric ratio) is a term relating the actual air to the theoretical minimum air required to complete combustion.

11 11 Terminology n Excess air is the amount of air supplied for combustion in "excess" of that theoretically required for complete combustion. This additional air is required because of imperfections associated with the combustion process and the practical limitation of providing the Three T's of Combustion.

12 12 Overfire Air zone 1 zone 2 overfire air fuel/air mixture in the overfire air to complete the combustion process. zone 2: Bring in 15-25% of total air combustion air to burn fuel under less than stoichiometric conditions. zone 1: Bring in 75-85% of total fuel/air mixture Secondary Furnace Primary Furnace _______________________________________________________________________

13 13 How OFA System Reduces NOx U1&2 n Fuel-rich combustion zone è The reducing environment helps control fuel and thermal NOx è The lower peak flame temperature helps further reduce the formation of thermal NOx n Overfire air zone è Thermal NOx formation is limited due to lower gas and flame temperatures

14 14 How OFA System Reduces NOx U3&4 n Fuel-rich zone è Withholding air causes the cyclones to be operated fuel-rich. As a result, CO is produced within the cyclone. In the lower furnace, this CO aggressively reduces already formed NOx to N2 in its attempt to form CO2. è The lower peak flame temperature provides an additional incremental reduction in NOx. n Overfire air zone è Thermal NOx formation is limited due to lower gas and flame temperatures.

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16 16 Atmospheric Nitrogen NOx [O2], temp. Thermal NOx Mechanism Critical Temperature

17 17 Non SCR NOx Reduction Problems Reducing atmosphere caused: Accelerated tube wastage in primary furnace Had to find acceptable stoichiometric setting to limit wastage Severe erosion/loss of refractory on furnace floor. Large amounts of molten iron pooled on the furnace floor at a higher frequency. Suffered numerous tap throughs. Started with silicon carbide refractory. Experimented with other forms of refractory. High alumina, 5% chrome refractory seems to hold up best. Severe pluggage in convection pass. Added 6 electric sootblowers to keep area clean.

18 18 Selective Catalytic Reduction (SCR) Began operation in May, Operates from May 1 through September 30. Will be required to operate year round beginning in Therefore, it was decided not to install bypass ducts and dampers. Two reactor boxes (north and south) Sized to hold four layers of catalyst. Initial operation is with two layers. Third layer is to be installed in Spring of Fourth layer is for future use, perhaps for mercury removal. Catalyst supplied by Hitachi America Ltd. Plate type, titanium dioxide (TiO2) carrier impregnated with tungsten trioxide (WO3) and vanadium pentoxide (V2O5). 72 catalyst modules per layer (9 wide X 8 deep grid). Initial guarantee is for 16,000 hours of 90% NOx removal before third layer is added.

19 19 Selective Catalytic Reduction (SCR) Two draft booster fans were installed to overcome the new SCR system pressure drop. Located between the precipitator and the stack Howden “Variax” constant speed, single stage, horizontal, axial flow. Utilizes variable pitch blades for flow control. Blades are hydraulically controlled. Impeller diameter is 3.7 meters (146 inches). Operates at 895 rpm. Ammonia vapor system Urea brought in by truck Dissolved in water to a 40% by weight solution in a mix tank. Heated to 210 deg C (410 deg F) at kg/scm (400 psig) by steam in a hydrolysis reactor (hydrolizer). Steam comes from high pressure turbine exhaust. Produces ammonia and carbon dioxide.

20 20 Selective Catalytic Reduction (SCR) Ammonia vapor system (continued) Spent solution (recycle ~ 3% solution) is continuosly withdrawn from the hydrolizer, sent through an economizer and then to a recycle storage tank. It is then used in the mix tank to mix batches of urea solution. Gaseous ammonia and carbon dioxide leave the hyrdolizer vessel and feeds a dilution skid upstream of each catalyst box. Each skid has an ammonia flow control valve that meters the correct amount of ammonia to achieve desired NOx reduction. The rate of ammonia generation in the hydrolizer is controlled to maintain constant manifold pressure at the dilution skids. When the ammonia vapor gets to the dilution skid, it is diluted and mixed with air from dilution air fans. It is then injected into the duct through a grid of pipes upstream of the catalyst.

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22 22 Selective Catalytic Reduction (SCR) Problems Large particle ash (LPA) Large particles of ash carried through the ductwork settles out on the screens above the catalyst. As it accumulates it blocks off the gas path and finer ash then builds up as well. Creates a differential increase through the catalyst from ~ 50 kg/sqm (2 inches water) to ~ 96.5 kg/sqm (3.8 inches of water) at which time the unit has to be brought off line for cleaning of the catalyst. At 96.5 kg/sqm (3.8 inches of water) differential, the catalyst chamber is 50% blocked. Creates a problem for the booster fans to maintain desired economizer outlet pressure. Currently designing a hopper to install under the economizer to catch the large ash before it reaches the catalyst boxes. May incorporate a screen to catch and direct the ash to the hopper. Plan to install hopper in Spring of 2007.

23 23 Plant Information (PI) Screen

24 24 Flue Gas Desulfurization System Work has begun to build a flue gas desulfurization system on unit 5. Project has been postponed to an in service date of 12/31/2010. Chiyoda design from Japan Differs from the conventional spray tower scrubber in that it uses a jet bubbling reactor which sparges the flue gas into a lime slurry bath where 100% of the flue gas reacts with the lime slurry before bubbling off the top and leaving the reactor to the stack. Foundations have been completed for the reactor and a new 252 meter (826 foot) high stack.

25 25 Flue Gas Desulfurization System Designed to provide sufficient limestone slurry to absorb 98% SO2 from the flue gas. Allows the burning of 11.3 mgm SO3/kcal (7.5 lb SO2/Mbtu) coal Redundant 100% ball mill systems capable of grinding 40 tons of limestone per hour. 895 kw (1200 hp), 4kV motors, horizontal, wet, with steel grinding balls. SCR booster fans will be replaced with two Howden, 50% capacity axial fans, each rated at ~ 11.2 mw (15,000 hp). Gypsum will be produced at ~ 73 tons/hour and will be dewatered by one vacuum belt filter before being landfilled.

26 Conceptual Model for Scrubber Jet Bubbling Reactor Typical Spray Tower Gas is sparged into Liquid Liquid is sprayed to into Gas Jet Bubbling Layer Reservoir

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