Claims:We Claim:
1. A controller for controlling an air pollution control (APC) process, comprising:
a. In which a consumable is required to control emissions of a pollutant
b. The APC process having multiple process parameters (MPPs)
c. One or more of the MPPs being controllable process parameters (CTPPs) one of the MPPs being an amount of the pollutant (AOP) emitted
A. a defined AOP value (AOPV) representing a limit on an actual value (AV) of the emitted AOP, comprising:
a. An interface configured to receive a value corresponding to a unit cost of the consumable
b. A control processor configured with logic
(i) To determine a first cost of performing the APC process based on the received value corresponding to the unit cost of the consumable
(ii) To direct control of at least one of the one or more CTPPs based on a current value of that CTPP
2. The controller according to claim 1, wherein the at least one MPP includes the at least one CTPP.
3. The controller according to claim 1, wherein the control processor is configured with the further logic to determine a current cost of performing the APC process in real time
, Description:Technical Field of the Invention
The present invention relates generally to process control. More specifically, the invention relates to techniques for enhanced control of processes, such as those used in air pollution control.
Background of the Invention
Wet Flue Gas Desulfurization:
As noted, there are several air pollution control processes, to form a basis for discussion; the WFGD process will be highlighted. The WFGD process is the most commonly used process for removal of SO2 from flue gas in the power industry. A depicting an overview of a wet flue gas desulfurization (WFGD) subsystem for removing SO2 from the dirty flue gas, such as that produced by fossil fuel, e.g. coal, fired power generation systems, and producing a commercial grade by-product, such as one having attributes which will allow it to be disposed of at a minimized disposal cost, or one having attributes making it saleable for commercial use.
In the United States of America, the presently preferred by product of WFGD is commercial grade gypsum having a relatively high quality (95+% pure) suitable for use in wallboard, which is in turn used in home and office construction. Commercial grade gypsum of high quality (˜92%) is also the presently preferred by product of WFGD in the European Union and Asia, but is more typically produced for use in cement, and fertilizer. However, should there be a decline in the market for higher quality gypsum, the quality of the commercial grade gypsum produced as a by-product of WFGD could be reduced to meet the less demanding quality specifications required for disposal of at minimum costs. In this regard, the cost of disposal may be minimized if, for example, the gypsum quality is suitable for either residential landfill or for backfilling areas from which the coal utilized in generating power has been harvested.
Object of the Invention
The present object of the invention is for providing advanced air pollution control
Summary of the Invention
It will also be recognized by those skilled in the art that, while the invention has been described above in terms of one or more preferred embodiments, it is not limited thereto. Various features and aspects of the above described invention may be used individually or jointly. Further, although the invention has been described in detail of the context of its implementation in a particular environment and for particular purposes, e.g. wet flue gas desulfurization (WFGD) with a brief overview of selective catalytic reduction (SCR), those skilled in the art will recognize that its usefulness is not limited thereto and that the present invention can be beneficially utilized in any number of environments and implements. Accordingly, the claims set forth below should be construed in view of the full breath and spirit of the invention as disclosed herein.
Brief description of Drawings:
FIG. 1 depicts a functional block diagram of an exemplary MPC control architecture, in accordance with the present invention.
Detailed Description of Invention:
WFGD Subsystem Architecture
FIG. 1 depicts a functional block diagram of a WFGD subsystem architecture with model predictive control. The controller incorporates logic necessary to compute real-time setpoints for the manipulated MVs, such as pH and oxidation air, of the WFGD process. The controller bases these computations upon observed process variables (OPVs), such as the state of MVs, disturbance variables (DVs) and controlled variables (CVs). In addition, a set of reference values (RVs), which typically have one or more associated tuning parameters, will also be used in computing the setpoints of the manipulated MVs .
An estimator, which is preferably a virtual on-line analyser (VOA), incorporates logic necessary to generate estimated process variables (EPVs). EPV's are typically process variables that cannot be accurately measured. The estimator implements the logic to generate a real-time estimate of the operating state of the EPVs of the WFGD process based upon current and past values of the OPVs. The OPVs may include both DCS process measurements and/or lab measurements. For example, as discussed above the purity of the gypsum may be determined based on lab measurements. The estimator may beneficially provide alarms for various types of WFGD process problems.
The controller and estimator logic may be implemented in software or in some other manner. If desired, the controller and estimator could be easily implemented within a single computer process, as will be well understood by those skilled in the art.
Model Predictive Control Controller (MPCC)
The controller of FIG. 1 is preferably implemented using a model predictive controller (MPCC). The MPCC provides real-time multiple-input, multiple-output dynamic control of the WFGD process. The MPCC computes the setpoints for the set of MVs based upon values of the observed and estimated PVs. A WFGD MPCC may use any of, or a combination of any or all such values, measured by:
pH Probes
Slurry Density Sensors
Temperature Sensors
Oxidation-Reduction Potential (ORP) Sensors
Absorber Level Sensors
SO2 Inlet and Outlet/Stack Sensors
Inlet Flue Gas Velocity Sensors
Lab Analysis of Absorber Chemistry (Cl, Mg, Fl)
Lab Analysis of Gypsum Purity
Lab Analysis of Limestone Grind and Purity
The WFGD MPCC may also use any, or a combination of any or all of the computed setpoints for controlling the following:
Limestone feeder
Limestone pulverisers
Limestone slurry flow
Chemical additive/reactant feeders/valves
Oxidation air flow control valves or dampers or blowers
pH valve or setpoint
Recycle pumps
Make up water addition and removal valves/pumps
Absorber Chemistry (Cl, Mg, Fl)
The WFGD MPCC may thereby control any, or a combination of any or all of the following CVs:
SO2 Removal Efficiency
Gypsum Purity
pH
Slurry Density
Absorber Level
Limestone Grind and Purity
Operational Costs
The MPC approach provides the flexibility to optimally compute all aspects of the WFGD process in one unified controller. A primary challenge in operating a WFGD is to maximize operational profit and minimize operational loss by balancing the following competing goals:

Maintaining the SO2 removal rate at an appropriate rate with respect to the desired constraint limit, e.g. the permit limits or limits that maximize SO2 removal credits when appropriate.
Maintaining gypsum purity at an appropriate value with respect to a desired constraint limit, e.g. the gypsum purity specification limit.
Maintaining operational costs at an appropriate level with respect to a desired limit, e.g. the minimum electrical consumption costs.