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Performance Optimization and Diagnostics
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Power Plants often do not operate on ideal design conditions and deviate from the design efficiencies and heat rates. In an actual scenario, there are many parameters that impact the plant operations which either directly or indirectly influence deviations in the heat rates and efficiencies from its ideal values. Deviations in fuel properties and calorific value, variations in the process parameters due to equipment degradation, various leakages, fouling of boiler tubes, changes in the ambient values, badly tuned controller settings can cause undesirable impact on the overall plant performance.
A study published by US Environmental Agency, says application of advanced optimization technologies for heat rate optimization can make improvements up to 1.5% in boiler efficiency and intelligent soot blowing techniques helps in improving it up to 0.9%. While these are direct benefits, there are substantial indirect benefits of optimization like increase in equipment life and reduction in carbon footprints. Any plant operating with incorrect operating set points will impact the efficiency and heat rates, there by resulting in burning extra fuel for meeting the station demand. Hence, it is advisable to use advanced optimization solutions.
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ELTRIX Plant Performance Optimization & Diagnostics (POD) module provides a number of optimization and diagnostics functionalities for Gas fired and Coal fired power plants. When combined with ELTRIX Plant Performance Management (PPM) module, it gives a complete solution for Performance Analysis Diagnostics and Optimization (PADO). The various sub-modules of POD:
i) Plant Performance Optimization
- System Performance Optimization (SPO)
- Boiler Performance Optimization (BPO)
- Soot Blower Optimization (SBO)
- Combustion Process Optimization (CPO)
ii) Plant Performance Diagnostics
- Plant Alarm Diagnostics (PAD)
- Water Chemistry Management (WCM)
System Performance Optimization (SPO)
SPO module analyzes and optimizes the performance of various sub systems in power plant, such as boiler, turbine, condenser, feed heaters, de-aerator and auxiliary equipments. The benefits of optimizing the overall power plant system are maximum thermal efficiency, lowest possible emissions, reduction in total maintenance cost and improved reliability. The SPO modules works in conjunction with other modules like Performance monitoring (Reduced auxiliary Consumption), Soot Blower Optimization (Cleaner Furnace walls and Convective pass) and Boiler Performance Optimization (Reduction in CO and NOx Level). The benefits of SPO are:
- SPO along with BPOS enables complete plant optimization
- SPO covers optimization of turbine, condenser, feed water heaters and de-aerators
- The system recommends controllable parameter settings to optimize the given process operating between 50% and 100% load conditions.
- Overall, SPO assists in operating plant under optimum conditions
Boiler Performance Optimization (BPO)
Boiler Performance Optimization consists of Combustion and Soot Blower Optimization. The key features of Boiler Performance Optimization:
- Continuously tracks the real time efficiency of the boiler system and compares it with the expected boiler efficiency.
- In case of deviations, the system analyzes the root cause for the occurrence.
- It recommends the optimized set points to improve the boiler efficiency and optimize the fuel consumption.
- It reduces NOX emissions, while adhering to CO limits
Combustion Process Optimization (CPO)In order to maximize operational efficiency, the fuel consumption rate should match with the generator steam demand. To achieve this state, air and fuel flow must be controlled. Combustion optimization module optimizes the amount of air required for combustion based on the fuel properties. The module predicts the stoichiometric condition and adds excess air required for the complete combustion. In order to control the air flow, the module will provide the percentage (%) of damper opening set point to PA Fans and FD Fans. Further, depending on the plant demand, CPO module predicts the required fuel flow through fuel property prediction model.The objectives of combustion optimization are:
- Control of NOx to a desired set point
- Balancing of combustion
- Maximization of boiler efficiency
Fuel modeling is the first step in combustion optimization, which determines the properties of fuel in real time. Fuel modeling is done with historical data from plant by adopting neural network methodology. Historical data is further used for calculating the quantity of theoretical and excess air required for complete combustion. The calculated data provides the inputs for improving combustion efficiency and minimizes the fuel consumption.
Soot Blower Optimization (SBO)
Soot blowing is a necessary boiler cleaning procedure which aims at maintaining or improving the unit’s heat rate.SBO module is specifically designed and developed to compute the level of slag / soot formation in each heat transfer section of the boiler. This module further conveys to the operator section-wise requirement of optimal soot blowing.SBO facilitates assessment of fouling of heat recovery surfaces of the steam generator and recommends selective soot blowing for the fouled sections. This module obtains operating data and provides the information directly to plant controls through closed loop systems.The benefits of SBO are
- The system dynamically determines boiler cleaning actions
- Directs existing soot blowing control systems to take action in real-time to best meet the unit’s key performance indicators.
- It works in conjunction with existing soot blowing control and instrumentation system.
- The system is developed by using adaptive modeling and expert rules
- It then initiates strategic soot blowing sequences to minimize heat rate and process steam loss.
- It continuously calculates the actual heat transfer coefficient of each heat exchanger
Plant Alarm Diagnostics (PAD)
In a power plant under an anomaly condition, alarms get triggered. Tracking of alarms along with root cause should be logged and maintained. This will guide the operator to take necessary steps on event of a similar alarm occurrence. Thus, Alarm Diagnostic module plays a vital role in maintaining the track on the different alarms generated in the control system along with all the process values.
Once an alarm is detected, the root cause analysis program is triggered. The diagnosis decision tree is traversed and the possible cause for the alarm is identified.
Alarm diagnostics module involves the following three steps:
- Root Cause Analysis (RCA) in case of process abnormality.
- Decision support (DS) on corrective actions for process operation and maintenance.
- Time-Critical DS for alternative actions.
The overall goal of RCA and DS is to extract the necessary information from DCS-data for early assessment of abnormalities and provide efficient troubleshooting advice in process operation and for maintenance on demand.
An adaptive algorithm is used for root cause analysis of alarms. Once the alarm has occurred, the algorithm identifies the root cause of the event by exploring the defined list. This is done by evaluating a set of premises associated with the alarm condition and their influence over the event. The most likely causes for the alarm are listed with system’s confidence level (reliability index). After inspecting the unit, algorithm points out the actual cause back to the system. Based on the actual cause of alarm, the system reassigns the confidence measures and correlations between alarms, causes and their premises. With this adaptive nature, the root cause prediction by the system is expected to improve its accuracy over a period of time.
Water Chemistry Management (WCM)
It is a well-known fact that corrosion in steam generators is an area of significant concern to both the manufacturers and users. A primary objective of water chemistry management module is to avoid the internal boiler tube corrosion. This module helps to improve life of boiler parts, decrease consumption of chemical dosing, minimize scale formation in boiler tubes, and prevent carryover of impurities to turbine.
The system monitors the water and steam quality in different sections of a steam generator cycle. Based on the inputs received after monitoring of water and steam, WCM module diagnoses the potential causes of upsets in steam generator cycle chemistry and suggests corrective actions. After acquiring data from all the chemical analyzers, the module stores the history of analyzer data. Corrosion of boiler tubes and heat exchanger equipment is due to alkalinity (pH level) of boiler circulation water. Boiler water pH should be maintained between 9 - 9.5. Following parameters are monitored continuously from the analyzer instruments:
- Alkalinity of boiler water (maintaining pH)
- Specific conductivity of boiler water
- Cation conductivity
- Sodium level in boiler water
- Ammonia content
- Phosphate content
- Silica level
