Abstract:
An integrated system [ 1000 ] is described for reducing operating costs of power plants while keeping gaseous pollutants in exhaust flue gasses, such as Mercury (Hg), below acceptable limits. Controller [ 1800 ] monitors and controls operation of a scrubber [ 1300 ], activator injection system [ 1400 ], sorbent injection system [ 1500 ] and a filter [ 1600 ]. Scrubber [ 1300 ] provides a neutralizer to remove SO 2  emissions. Activator injection system [ 1400 ] provides and activator that increases affinity of the pollutant gasses for a sorbent. Sorbent injection system [ 1500 ] employs novel low friction injection lances [ 1590 ] that evenly distribute the sorbent particles. A filter [ 1600 ] collects the sorbent particles that cake onto filter bags [ 1620 ] that are periodically cleaned. A controller [ 1800 ] receives the costs of materials consumed and the filter bag life for the plant and performs an optimization of the multiple variables to minimize costs while keeping the pollutant emissions below a prescribed limit.

Description:
TECHNICAL FIELD 
     The present disclosure relates to a system for reducing gaseous pollutant emissions from a power plant, and more specifically an integrated optimization system for reducing gaseous pollutant emissions from a power plant while minimizing costs of plant operation. 
     BACKGROUND 
     Furnaces, such as commercial boilers, burn fuels that release gaseous pollutants, such as mercury into the atmosphere. Mercury condenses returns to the ground as a toxic contaminant. New regulations are proposed to greatly reduce the amount of mercury that can be released. 
     Devices have been employed that reduce the amount of mercury released. One such device disperses activated carbon particles into the flue gasses to adsorb the Mercury gasses. 
     When too much mercury is exiting the system, the system simply increases the amount of sorbent used. Sometimes other parameters that may be altered to achieve better results. 
     An activator is used in addition to a sorbent to decrease mercury emissions. Again, there are times when increasing the amount of activator used is not as effective as adjusting another input parameter. 
     In the past, there have been systems that optimized one or more parameters of the system. These however, did not take into account additional parameters that may be varied to adjust the emissions of mercury from a plant, and did not optimize all the parameters. They also did not optimize with respect to plant operation costs. 
     With the prior art systems, there may be additional use of sorbent or activator. This results in waste and additional plant operation costs. 
     Currently there is a need for a system that optimizes the important parameters, insures that gaseous pollutant emissions are below an acceptable set level and that minimized plant operation costs. 
     SUMMARY 
     The present invention may be embodied as An optimized pollutant removal system [ 1000 ] in a boiler system burning a fuel, functioning to reduce operating costs while maintaining pollutants of a flue gas stream below an acceptable limit comprising: 
     a scrubber [ 1300 ] for dispersing a neutralizer into the flue gas stream removing SOx gasses; 
     a sorbent injection subsystem [ 1500 ] having a sorbent chamber [ 1550 ] for receiving said flue gas stream, the sorbent injection system [ 1500 ] adapted to disperse sorbent particles within the flue gas stream at a defined rate, the sorbent particles adapted to adsorb gaseous pollutants; 
     a filter [ 1600 ] coupled to the sorbent chamber [ 1550 ] for filtering the sorbent particles having adsorbed gaseous pollutants out of the flue gases; 
     a stack [ 1700 ] coupled to the filter [ 1600 ] for releasing the filtered flue gases; 
     a stack sensor [ 1710 ] for monitoring an amount of gaseous pollutant exiting the stack [ 1710 ]; 
     a controller [ 1800 ] coupled to the scrubber [ 1300 ], the sorbent injection subsystem [ 1500 ] and the stack sensor [ 1710 ] for reading the rate that neutralizer is provided into the flue gasses, the rate of the sorbent is dispersed by the sorbent injection subsystem, an amount of gaseous pollutant in the stack [ 1700 ], a unit cost of the neutralizer, the sorbent and for providing a signal adjusting the rate of neutralizer and sorbent dispersed to reduce said boiler operating costs while maintaining gaseous pollutant levels within predetermined acceptable levels. 
     The present invention may also be embodied as a controller [ 1800 ] for use in a boiler having a scrubber [ 1300 ], an activator system [ 1400 ], a sorbent injection system [ 1500 ], a filter [ 1600 ]), the controller [ 1800 ] adapted to: 
     monitor the scrubber [ 1300 ] operating parameters neutralizer material being consumed; 
     monitor activator system [ 1400 ] operating parameters and activator material consumed, 
     monitor sorbent injection system [ 1500 ] operating parameters and sorbent material consumed; 
     monitor pollutant emission parameters, 
     monitor opacity parameters in the stack [ 1700 ], 
     calculate actuator parameters for the activator system [ 1400 ], scrubber [ 1300 ], sorbent injection system [ 1500 ] and filter [ 1600 ] corresponding to a minimum operating costs while maintaining emissions below a predetermined acceptable level, based upon the monitored parameters and the cost of material consumed. 
     The present invention also includes an injection lance [ 1590 ] extending in a general vertical direction for dispersing a powdered material into a flowing flue gas traveling generally horizontally, the injection lance [ 1590 ] comprising: 
     a plurality of conduits [ 1591 - 1599 ] each having: 
     a first end [ 1571 - 1579 ] for receiving said powered material, and 
     a second end [ 1581 - 1589 ] for releasing powdered material into said flowing flue gas, 
     at least two conduits [ 1591 - 1599 ] having different lengths, and 
     the conduits attached together in a manner such that the first ends [ 1571 - 1579 ] are generally coplanar, and the second ends [ 1581 - 1589 ] are offset vertically from each other. 
     OBJECTS OF THE INVENTION 
     It is an object of the present invention to provide an interactive control system that monitors several parameters of the furnace and adjusts several inputs to the furnace to keep pollutant gas levels below an acceptable value, while minimizing plant-operating costs. 
     It is another object of the present invention to provide an interactive system that controls several aspects of the system to control pollutant gas emissions. 
     It is another object of the present invention to provide an interactive system that monitors and optimizes the absorptive material injected into the flue gasses to minimize pollutant gas emissions. 
     It is another object of the present invention to provide an interactive system that monitors and optimizes the amount of activator material injected onto the solid fuel to minimize mercury emissions. 
     It is another object of the present invention to provide an interactive system that monitors and optimizes both the absorptive material injected into the flue gasses and the activator material added to the solid fuel to minimize mercury emissions. 
     It is another object of the present invention to provide an interactive system that monitors and optimizes system functioning to minimize costs of materials used. 
     It is another object of the present invention to provide an interactive system that monitors and controls both the SO 3  and SO 2  emissions to facilitate mercury removal and reduce mercury emissions. 
     It is another object of the present invention to provide an interactive system that monitors and controls system functioning to maximize filter bag life. 
     It is another object of the present invention to inject sorbent material that is more resistant to clogging as compared with prior art injection systems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the drawings, wherein like items are numbered alike in the various Figures: 
         FIG. 1  is a simplified schematic diagram of a coal-fired boiler employing sorbent injection into the flue gasses that, that is optimized according to the present invention. 
         FIG. 2  is an exploded perspective view of one embodiment of an injection lance according to the present invention. 
         FIG. 3  is a plan view and side elevational view of a base plate and conduits of one embodiment of the injection lance shown in  FIG. 2 . 
         FIG. 4  is a plan view and side elevational view of a restrictor plate of one embodiment of the injection lance shown in  FIG. 2 . 
         FIG. 5  is a perspective view of a splitter compatible with the present invention. 
         FIG. 6  shows both a side elevational view and a plan view of the bottom of the splitter shown in  FIG. 5 . 
         FIG. 7  is a partial perspective view of a fabric filter subsystem compatible with the present invention. 
         FIG. 8  is a schematic showing the inputs and outputs of one embodiment of a controller  1800  consistent with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Theory 
     Solid particles suspended in flowing flue gases have been known to be separated from the remaining flue gasses with the use of fabric filters and/or electrostatic particle filters. Fabric filters physically stop particles of a given size or larger from passing through the fabric to escape. The particles are collected from the outside of the filter then disposed. 
     Electrostatic filters precipitate solid particles out of the flue gases by using electrostatic attraction. 
     Gaseous pollutants are more difficult than particulate matter to remove from escaping flue gasses. Mercury (Hg) is present in many fuels, such as coal. When coal is burned, Hg is released into its gaseous phase. Hg is a toxic pollutant and should be removed from the flue gasses. 
     Adsorption of gaseous pollutants, such as Hg, are based upon a) proximity of the gaseous pollutant molecules to the adsorption particles; and b) excitation of the pollutant gas molecules. 
     One method of removing gaseous pollutants is to disperse a sorbent agent, such as activated carbon into the Hg gas. Activated carbon adsorbs Hg gas. 
     Proximity is the collective separation between the adsorbent particles the Hg gas molecules. This depends upon particle distribution in the volume. Greater proximity may be achieved by directing more sorbent material to regions where Hg converges. Greater distribution of sorbent near the Hg allows the particles to become available for adsorption of the Hg gas. 
     The amount of adsorption also is dependent upon the attraction between the molecules on the surface of the adsorbent particles and the Hg molecules. It has been known that treating the Hg gas with activators, such as Calcium Bromide (CaBr 2 ) and bromine, increase the affinity of Hg gas for the molecules on the surface of the adsorbent particles. This is referred to as activation of the Hg molecules. 
     Competing Molecules 
     Since Hg competes with other molecules for the active adsorption sites on the surface of the adsorbent particles, Hg adsorption increases with decreasing amount of competing molecules. SO 2  and SO 3  are created from burning fuels, especially coal. These molecules are also adsorbed into the adsorbent and compete for sites on the surface of the adsorbent particles. SO 3  is much more reactive with the sorbents as compared with SO 2 . Therefore, minimizing the SO 3  concentration in the flue gas greatly increases Hg adsorption. Minimization of SO 2  also increases Hg adsorption, but not to the extent of minimizing SO 3 . Therefore, one of the main goals is to minimize SO 3  in the flue gas to a low level, such as less than 10 parts per million (ppm). 
       FIG. 1  is a simplified schematic system diagram of a coal-fired boiler  1000  employing sorbent injection into the flue gasses that is optimized according to the present invention. 
     Hot flue gasses pass through exhaust duct  1110  and into the flue gas side  1210  of heat exchanger  1200 . Air enters the system  1000  and is preheated in preheat side  1220  of a heat exchanger  1200 . 
     The hot flue gasses enter a scrubber  1300 . A neutralizer, such as CaCO 3 , is provided by blower  1310  into the flue gasses. The neutralizer removes the SO 2 , SO 3  from the flue gasses. Excess neutralizer falls to a collection section  1350  that is collected for recirculation. 
     A sensor  1320  monitors the amount of neutralizer provided by blower  1310 . 
     The flue gas then exits scrubber  1300  at outlet  1380  and passes into inlet  1551  of sorbent chamber  1550 . This may be a duct, or it may be a chamber specifically designed for its use. A sorbent, such as activated carbon, is held in a silo  1510 . Sorbent is passed to a sorbent pump  1520  that blows it into a distributor  1540 . Distributor  1540  distributes the flowing sorbent to at least one injection lance  1590 . Injection lance  1590  has a unique design that allows even distribution of sorbent throughout the sorbent chamber  1550 . Since sorbent is used to adsorb gaseous Hg, it is important to spread out the particles to create a large effective surface area to capture as many Hg molecules as possible. 
     As discussed above, an activator may be used to increase the affinity of Hg molecules to the sorbent particles. One such way is to spray the activator onto the solid fuel being used. In this example, bulk coal  3  is placed on a conveyor  5 . An activator in activator storage  1410  is passed to an activator flow controller  1420 . This may be a pump or valve that can be controlled that meters a desired amount of activator and provides it to the bulk coal  3 . 
     The activator and bulk coal  3  are then provided to a crusher  7  that pulverizes them into pulverized coal with activator, simply referred to as pulverized coal. The pulverized coal is provided to the boiler  1100  along with heated air for combustion. 
     An activator flow control  1420  may be a metering pump that is used to monitor the activator flow rate. This monitored information is used later in optimization. 
     The sorbent and activator adsorb the Hg gas and are passed with the flue gas to a filter  1600 . This may be a fabric filter, an electrostatic filter, or other filter that is capable of filtering the sorbent and flyash out of the flue gasses. Flue gasses enter through the filter inlet  1610 . They then pass from the outside of each filter bag to the inside. Once inside the filter bag, they are allowed to exit through the filter outlet  1690 . 
     The filter  1600  removes the particulate matter from the flue gas. The sorbent, with the adsorbed Hg molecules and flyash are collectively referred to as a ‘filter bed’. The filter bed accumulates on the outside surface of the filter bags  1620 . The thickness of the filter bed is important in removing additional Hg molecules. 
     Sorbent Dispersion 
     As stated above, the dispersion of the activated sorbent has an effect on Hg removal efficiency. The more dispersion, the more surface area contact between the activated charcoal and the flue gasses. Therefore, it is important to provide maximum dispersion of the sorbent in the flue gasses to increase efficiency. 
       FIG. 2  is an exploded perspective view of one embodiment of an injection lance according to the present invention. 
       FIG. 3  is a plan view and side elevational view of a base plate and conduits of one embodiment of the injection lance shown in  FIG. 2 . The lance of the present invention will be described in connection with both  FIGS. 2 and 3 . 
     This lance has a ‘skyscraper’ shape wherein a number of elongated conduits  1591 ,  1592 ,  1593 ,  1594 ,  1595 ,  1596 ,  1697 ,  1598 , and  1599  can be seen here. The conduits are fixed with respect to each other and fit within a central opening  1567  of a base plate  1566 . The conduits  1591 - 1599  have least two having differing lengths. These are all substantially parallel to each other and are vertically aligned. They each have a first end opening  1571 ,  1572 ,  1573 ,  1574 ,  1575 ,  1576 ,  1577 ,  1578 , and  1579  that is vertically higher than a second end opening  1581 ,  1582 ,  1583 ,  1584 ,  1585 ,  1586 ,  1587 ,  1588 , and  1589 . 
     The first ends are substantially aligned, causing the second ends to extend various lengths down the lance terminating at different vertical locations. Sorbent particles are provided into their first end openings  1571 - 1579 . The sorbent particles travel through the length of the conduits and out the second end openings  1581 - 1589 . Since these are aligned generally in a vertical direction, gravity partially pulls the particles down and out of the conduits  1591 - 1598 . Since the particles exit at different vertical exit points, there is a greater distribution of particles over the sorbent chamber volume. 
     These conduits  1591 - 1599  are preferably straight since straight conduits exhibit the lowest resistance to flow. Also, the lances  1590  preferably have no narrowed sections. There is also little pressure required to pass the particles through conduits having these properties, since gravity is pulling the particles downward through the conduits. 
     The injections lances  1590  are aligned generally vertically having a forward edge meeting said oncoming flue gas stream. 
     A wear protector  1588 , shown here as two flat strips meeting at an angled edge acts as the leading edge  1555  of the lance  1590 . Flue gasses are directed at the lances  1590  first encounter the angled edge of the wear protector  1588 . This protects the lances from the oncoming flue gasses. It reduces wear of the lances  1590  and provides rigid structural support. 
     Wear protector  1588 , by its shape causes turbulence behind it facilitating the dispersion of adsorbent particles released from the trailing edge  1557  of the lance  1590 . This turbulence near the trailing edge of injection lance  1590  further distributes the sorbent particles over the volume of sorbent chamber ( 1550  of  FIG. 1 ). 
     The longest conduits  1595 ,  1594  are located near the leading edge  1555  with the shorter ones located near the trailing edge  1557  to provide a plurality of second end openings  1581 ,  1582 ,  1583 ,  1584  and  1585  on the trailing edge of the injection lances  1590 . 
     Since the system employs a low-pressure distribution of the particles, smaller particles may be distributed which have increase surface area. The straight flow, low pressure conduits have no curves or angles and therefore significantly reduce amount of clumping of particles. This results in less clogging and reduced maintenance time and cost. 
     It is envisioned in this invention that the conduits  1591 - 1599  may alternatively have cross sectional shapes other than square or rectangular, be angled with respect to a vertical line, may include some curves, and/or may have one or more narrowed sections. These will reduce their performance of the lances  1590 , but still remain functional and within the scope of this application. 
     Optionally, as shown in  FIG. 3 , each conduit may be ‘tuned’ to insure that there is the same resistance to flow. One or more tuning inserts  1587  can be inserted into selected conduits. These balance the flow among the conduits. Various sized tuning inserts  1587  may be used to properly adjust the flow resistance so that there would be an even distribution of particles. Since they are exposed to a great deal of erosion, they should be made of an erosion resistant material, such as ceramic. 
       FIG. 4  is a plan view and side elevational view of a restrictor plate  1568  of one embodiment of the injection lance shown in  FIG. 2 . The restrictor plate has holes  1569  designed to line up with the conduits  1591 - 1599 . The holes  1569  are sized to more accurately control the amount of materials passing thorough the lances  1590 . 
       FIG. 5  is a perspective view of a splitter  1900  compatible with the present invention. Splitter  1900  has a main feed section  1901  that receives flowing air and the sorbent. The sorbent may have an activator in it. The flowing air and sorbent are split evenly into a plurality of lance feeds  1903 . The lance feeds  1901  each connect to and feed an injection lance, not shown here. 
       FIG. 6  shows both a side elevational view and a plan view of the bottom of the splitter  1900  shown in  FIG. 5 . Several branched pathways  1905  are visible. Each of these branched pathways  1905  leads to a different lance feed  1903 . The splitter  1900  results in a device for evenly distributing air and sorbent in an even manner to all of the injection lances. 
     Control System 
     There have been systems that monitored and optimized a single aspect of the system. However, adjusting one parameter may have consequences on other aspects of the system. Therefore, it is important to monitor multiple aspects, weight them by their relative costs, then adjust several output parameters to minimize the plant operating costs. 
     The amount of neutralizer provided to the flue gas controls the amount of SO 2 , SO 3  left in the flue gasses. The SO 2 , SO 3  competes with the Hg for sites on the sorption particles, decreasing the amount of Hg adsorbed. Increasing the amount of limestone neutralizer decreases the amount of SO 2  and SO 3  molecules in the flue gas. However, too much neutralizer results in waste that adds to the cost of operating the plant and should also be minimized. 
     The present invention also functions to reduce waste, by optimizing the amount of sorbent material used. More sorbent results in a more concentrated dispersion in the sorbent chamber  1550 . This result in more Hg adsorbed. However, too much sorbent results in additional unnecessary operation costs. 
     There should be enough activator provided to the system to properly activate the Hg molecules. However, additional activator should be eliminated to reduce waste. 
     Optimize Filter Bed Depth 
     Flyash and sorbent collects on the outside surface of fabric filters. This creates a ‘filter bed’. The filter bed thickness increases over time as more sorbent and flyash collects. The Hg gas molecules must travel through the filter bed to exit the system. Thicker filter beds increasing the amount of contact that the Hg gas has with the adsorbent particles. The more contact, the greater the probability that the Hg gas molecules are adsorbed into the sorbent in the filter bed. However, the thicker the filter bed, the more resistance there is to flue gases exiting the system. 
     The filters are designed to be self-cleaning. U.S. Pat. Nos. 6,022,388 Andersson et al. Feb. 8, 2000 “Device for Cleaning Filter Elements”, 6,749,665 B2 Bjarno et al. “Method When Cleaning A Filter”, and International Patent Application PCT/SE92/00453, Applicant ABB Flakt collectively describe a device and method for removing or reducing the thickness of the filter beds on the fabric filters. These filter cleaning subsystems may be used with the present invention. 
     Different filter bed thickness causes different mercury adsorption levels. Therefore, it is best to monitor and adjust filter bed thickness to optimize mercury adsorption as well as flue gas flow. The filter bed thickness may be adjusted by adjusting the amount of sorbent being used and/or cleaning the filter bags. 
     Optimize Filter Bag Life 
     In the Andersson patent above,  FIG. 1  is recreated here as  FIG. 7 . This illustrates how self-cleaning fabric filters function. Air enters through each of the filter bags  1620 . Gases pass through the filter bags  1620 , but particulate matter is stopped and collects on the surface of filter bags  1620 . 
     The air, without suspended particles, exits as shown by the open arrows “P 1 ”. The particulate matter collects on the outside surface of the filter bags  1620  creating a filter bed. The thickness of this filter bed is referred to as “filter bed depth”. 
     Once the filter bed depth has grown past a threshold level, it is removed. One such method is to activate an air pump ( 1650  of  FIG. 1 ). This provides air-to-air valves ( 1660  of  FIG. 1 ). When the air valves open, a burst of air is provided to the inside of filter bags  1620  from air nozzles  1670 . Air nozzles  1670  blow air in a direction marked by arrow “P” that is opposite the normal flue gas flow direction. The air is quickly discharged into the filter bags  1620  to create a burst of air from inside which blows the accumulated filter bed off of the outside of the filter bags  1620 . The filter bed falls to the bottom of the filter  1600  and is collected. 
     The more often bursts of air are discharged into the filter bags  1620 , the shorter the lifespan of the filter bags  1620 . Once the filter bags  1620  have become too worn, or break, they have to be replaced. This requires maintenance time and expenses are incurred for the service and materials. Also, there is lost production time if the system is shut down during the maintenance. Therefore, it is advantageous to how much life is left in a filter bag so that it may be replaced when another is being replaced if there is not much life left in the bag. This saves considerable maintenance costs. 
     Therefore, another goal is to optimize the frequency of air bursts provided to the filter to keep the filter functioning properly, maximize the filter bag life while keeping the Hg emissions within the acceptable limits. 
     Controller Inputs 
     Referring both to  FIGS. 1 and 8 , to achieve the goals above, a controller  1800  monitors several system inputs and controls several system outputs. 
     The SO x  levels are monitored by SO x  sensors  1565  located at the inlet  1551  of sorbent chamber  1550 . Since the SO x  compete with Hg for the sorbent sites, the SO x  should be removed prior to injection of the sorbent. This translates to the sorbent injection being downstream from the SO x  removal portion of the system. 
     The air temperature and air flow rate are measured by air temperature sensor  1561  and air flow sensor  1563  at inlet  1551  of sorbent chamber  1550 . 
     A sorbent flow sensor  1530  measures the rate at which sorbent is being fed into the system. 
     An activator flow sensor  1430  measures the rate at which an activator, such as calcium bromide, is being fed into the system. 
     An Hg emissions sensor  1710  on the stack  1700 . In this example, the emissions sensor  1710  monitors Hg gas. 
     An opacity sensor  1720  in the stack  1700  measures the opacity of the flue gases being released from the stack  1700 . 
     A inner filter sensor  1640  measures the pressure inside of the filter bags  1620 . An outer filter sensor  1650  measures the pressure just outside of the filter. These sensors report the pressure readings to the controller  1800 . Controller  1800  calculates a differential pressure indicating the amount of flue gas flow through the filter and the filter bed thickness. 
     The current cost for neutralizer per unit volume is input to the controller  1800 , as is the cost for activator and the sorbent. Also, the cost of filter bags adjusted for their usable life are provided to controller  1800 . These will be used to calculate the actual operating costs for a plant. 
     Controller Outputs 
     The controller  1800  reads data from the input sensors, and uses the data provided to it, to determine the combination of outputs that will minimize operating costs while keeping emissions within the acceptable limits. 
     The calculations are performed by a controller  1800  according to known methods of reading in data from one or more sensor and providing output signals to one or more actuators to create a monitored output less than a threshold level. 
     This is also described in U.S. Pat. No. 7,117,046 B2 Boyden et al., Oct. 3, 2006 entitled “Cascaded Control of an Average Value of A Process Parameter To A Desired Value”, which is hereby incorporated by reference as if set forth in its entirety herein. 
     Similar parameter optimization systems are described in U.S. Pat. Nos. 7,398,652 B1 Kosvic et al., Jul. 15, 2008 “System for Optimizing a Combustion Heating Process”, 7,123,971 B2 Piche, Oct. 17, 2006 “Non-Linear Model With Disturbance Rejection” and/or 5,623,402 Johnson Apr. 22, 1997 “Multi-Channel Inverse Control Using Adaptive Finite Impulse Response Filters”. 
     Controller  1800  reads the input data from the sensors. It then calculates a trim signal for neutralizer blower  1310  to adjust the amount of neutralizer provided to the flue gasses in scrubber  1300  to provide the maximize SOx removal while not wasting the neutralizer. SOx should be minimized since they affect the ability of the sorbent to function. 
     The Controller  1800  calculates from the current cost of the sorbent, activator and neutralizer, and the flow rates of sorbent, activator, the additional amounts of neutralizer to be used and the timing to pulse the filter bags  1620  to keep the Hg emissions within the acceptable limits for the lowest operating cost. 
     Controller operates sorbent pump  1520  to provide the calculated sorbent flow rate. 
     Controller  1800  runs the activator flow control  1420  to provide the calculated activator flow rate. 
     Controller  1800  also provides a pulse signal to pulse air valves  1660  of filter  1600  to maintain the optimum filter bed depth. 
     Based upon the number of times that the filter bags  1620  have been cleaned, the pressures measured inside and outside of the filer bags  1620 , and the opacity measured in the stack  1700 , an estimation of the remaining filter bag life is determined. This estimation is calculated by controller  1800  and provided to a plant operator on a user interface  1810 . 
     Based upon the pressures measured inside and outside of the filer bags  1620 , and the opacity measured by the opacity sensor  1720  in the stack  1700 , a determination is made that the filter bag  1640  failed. If it has, an indication is provided to the plant operator on user interface  1810 . 
     The Controller  1800  interactively calculates from the current cost of the sorbent, activator and neutralizer, and the actual flow rates of sorbent, activator, the additional amounts of neutralizer to be used and the timing to pulse the filter bags  1620  the actual costs to keep the Hg emissions within the acceptable limits. These costs are provided to the plant operator on the user interface  1810 . 
     Although the invention has been described and illustrated with respect to exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto, without parting from the spirit and scope of the present invention. Accordingly, other embodiments are within the scope of the following claims.