Testing and measurement (T&M) solutions are needed to operate power generation plants safely, productively, and in an environmentally friendly manner. They play a vital role in extending the asset life and in the early detection of failures, thereby minimising equipment outage. The implementation of these solutions involves the deployment of sensors, transmitters and related equipment for tracking the desired plant parameters such as water quality, pressure, temperature, flow, emissions, and combustion efficiency. This requires several critical measurements, from combustion performance and water chemistry to stack emissions, to enhance the operational efficiency of power plants, lower emission levels, and optimise operations and maintenance. In renewable energy plants, T&M is helpful in monitoring condition, structural health system architecture, etc. For hydropower projects, especially pumped storage plants, testing is becoming a key focus area for gencos to determine the hydraulic/electrical efficiency of the units, fulfil contract guarantees and reduce contractual disputes.
Power Line takes a look at some of the T&M solutions being deployed by gencos…
Thermal power plants
- Emission and effluent monitoring: For online monitoring of emissions and effluents, continuous emission monitoring system (CEMS), predictive emission monitoring system (PEMS), continuous effluent quality monitoring system (CEQMS) and continuous ambient air quality monitoring system (CAAQMS) technologies are being deployed by gencos. CEMS/PEMS and CEQMS are real-time air and water pollution monitoring systems respectively. CEMS technology involves the use of SO2, NOx and particulate matter analysers for stack emission while in CEQMS technology pH, TSS and temperature analysers are deployed for effluent monitoring in all the operating stations/units. The Central Pollution Control Board has mandated the installation of CEMS for real-time pollution monitoring of stack emissions and CEQMS for effluent quality monitoring in 17 categories of highly polluting industries, including power plants. Meanwhile, CAAQMS is used for monitoring the ambient air quality in real time. Besides these, mercury analysers are deployed for emission monitoring wherever stipulated.
- CEMS: It deploys complex extractive analysers, which remove flue gas samples from the duct and use a series of individual gas sensor modules or more advanced spectroscopic techniques to determine the composition. It is preferable to analyse flue gas as close to the combustion process as possible. Such in-situ analysis can take the form of sensors placed directly in the flue gas, or line-of-sight optical absorption measurements, for which a transmitter and a receiver are placed on either side of the duct or furnace. CEMS technology provides continuous measurement of data on a real-time basis at the monitoring site of interest, and enables immediate corrective/preventive measures in case of any disturbance. Hence, it can help gather real-time data, and allow plant operators to remotely access plant performance as well as conduct continuous performance checks on air pollution control devices.
In the adoption of CEMS, utilities face challenges in terms of choosing between different monitoring systems and instruments, different suppliers and multiple data formats, multiple platforms and communication protocols, and different data collected from heterogeneous systems. To overcome this issue, there is a need to have coherence between central and state regulatory systems, clarity in the CEMS audit protocol and a compliance mechanism.
PEMS: PEMS is the next level of emission monitoring and does not use hardware-based sensors to measure emissions. It uses unique algorithms to predict the emissions of a plant, based on the input parameters. While there are standalone versions of PEMS available, these systems are widely used as part of an integrated environmental monitoring approach, capable of addressing multiple sources in a plant. When combined with data acquisition and handling systems, and integrated in plant-wide IT and communications networks, PEMS can be a viable diagnostic tool for lowering emissions and improving combustion efficiency.
- Combustion efficiency: Efficient fuel combustion is essential for cutting operating costs and reducing emissions from power plants. For efficient combustion, the ratio of air to fuel is a critical factor. Insufficient air leads to incomplete combustion, resulting in emission of soot, smoke and carbon monoxide, while excessive air reduces the overall boiler efficiency. The solution is to measure flue gas oxygen. The level of oxygen present in the combustion of waste gas is a key indicator of the amount of air supplied to the process. It can be monitored by using combustion gas oxygen analysers, which accurately measure the oxygen content in the combustion gas. Furthermore, these analysers can be used in conjunction with flow meters to regulate the amount of air supplied to the burner.
- Boiler efficiency: To achieve the optimum performance of a coal-fired power plant, careful monitoring of the quality of water and steam in the feedwater is essential. Several chemicals need to be monitored and controlled for optimum steam raising efficiency. Dissolved oxygen in the feedwater can cause pitting in the boiler and reduce its operating life. Dosing the feedwater with hydrazine can reduce oxygen to form nitrogen and water. At high temperatures and pressures, ammonia is formed, which raises the feedwater pH level, increasing the risk of corrosion. Further, silica can hamper heat transfer efficiency and increase the risk of turbine malfunction by its precipitation on the blades. The solution includes pH analysers for monitoring feedwater acidity or alkalinity. By indicating the level of contamination, the type and duration of treatment can be determined.
Renewable energy plants
With the growth of renewable energy capacity, there will be an increase in demand for the T&M of renewable energy equipment including solar cells, solar photovoltaic (PV) modules, and wind turbine generators, besides hydropower plants.
- Solar: Monitoring of solar PV plants can be done in both ways, that is, by using human workforce or by using remote monitoring systems. The monitoring methods to be adopted could vary depending upon the size of the power plant and the site at which the plant is located. However, remote monitoring is preferred as it leads to reliable operation, better operations and maintenance, and improved output performance of the PV plant. For this, sensors, signal processing units, data transmission, data storage and logging facilities, and cloud-integrated data analytics are deployed. These help in condition as well as structural monitoring of solar plants and facilitate planned maintenance with deep insight into the component failures before they affect energy production.
- Wind: In case of wind generators, condition monitoring of structural components, such as foundations, blades and towers, is critical, as failure of structural components can affect the operational costs. Offshore wind turbines are particularly exposed to the harsh environments and are at a higher risk. Therefore, it is essential to monitor the structural components to reduce maintenance costs and avoid catastrophic failures. Besides this, condition monitoring of wind turbines is important to detect changes in the turbine behaviour and predict faults so as to minimise performance degradation and cost. The most commonly used sensors for wind turbine condition monitoring include accelerometers, temperature sensors, pressure sensors, rotational speed sensors, and current clamps.
- Hydro: In June 2023, the Central Electricity Authority notified the guidelines for field efficiency test in hydropower plants including pumped storage projects. The guidelines will be applicable to any size/type of unit, comprising a generator–motor, an impulse/reaction turbine and a pump-turbine with a unit size greater than 5 MW. These guidelines specify a generator/motor field efficiency measurement test to verify the efficiency of synchronous generators/induction machines at site; and a turbine/pump efficiency measurement test. For these, instruments including flowmeters (to check the flow rate of fluids), thermal detectors (to determine the temperature rise of the liquid coolant) and coolers (calorimeters needed for the bearing oil, and for the cooling water of air- or gas-coolers) will be utilised. Further, for measuring electrical quantities, instruments such as micro-ohm meters for resistance measurement, digital power analysers, three–phase digital wattmeters, and digital multi–function meters shall be utilised.
Remote monitoring systems
Drones are being increasingly deployed to remotely monitor power plants as they can track changes in performance over time. The use of drones for inspection offers several advantages such as evaluation of the power plant condition, monitoring of inaccessible areas, reduced plant downtime and maintenance costs, and safety of power plant personnel. Drones are also relevant for monitoring of power stations with flue gas desulphurisation equipment. Further, lining failure due to inadequate material quality or faulty workmanship, or even localised damage, can lead to immediate corrosion and, possibly, structural damage. During a unit outage, drones can be operated inside the chimney to provide a comprehensive, high resolution image of the internal lining system.
Gencos are also keenly opting for control solutions that enable them to monitor and control equipment parameters through automation. For example, ML-algorithms have gained traction for intelligent fault detection, predictive maintenance capabilities as well as monitoring of the whole compressor system from the same human-machine interface used for conventional process control. The T&M sector will witness many developments in the coming years due to the path-breaking innovations in recognition technology, artificial intelligence and machine learning. Further, internet of things enabled T&M instruments will gain traction going ahead.
Conclusion
T&M solutions for power plants are necessary to identify and address challenges related to performance in real time. They help in maintaining the operational efficiency of a power plant as well as lowering emission levels. Further, they are useful in enhancing the life of power plant equipment, and in avoiding lapses in preventive and predictive maintenance that can lead to unsafe conditions, system breakdown, and revenue loss. However, the right combination of T&M equipment plays a vital role in checking the health of the critical power plant equipment. Going forward, the adoption of comprehensive T&M solutions for power plants will help utilities repair or replace faulty units in real time.