How Can H/J Class HRSG Boilers Meet the Efficiency and Safety Requirements of Combined Cycle Power Generation?

Why H/J Class HRSG Boilers Become Core Equipment in Combined Cycle Power Generation

In natural gas combined cycle power generation and gas-steam combined cycle systems, H/J class HRSG (Heat Recovery Steam Generator) boilers have emerged as the core hub connecting gas turbines and steam turbines, thanks to their efficient waste heat recovery capabilities and stable steam output. Their core advantage stems from optimized design for high-temperature flue gas— the heating surfaces (such as economizers, evaporators, and superheaters) of H/J class HRSGs are arranged in multiple layers, enabling full absorption of heat from high-temperature flue gas (typically 500-600℃) discharged by gas turbines. This heat converts water into high-pressure, high-temperature steam (with pressure up to 10-15MPa and temperature exceeding 500℃), which is then transported to steam turbines for power generation. This realizes dual energy recovery of “gas power generation + waste heat reuse,” boosting the overall power generation efficiency by 15%-20% compared to conventional coal-fired units. Compared to regular HRSGs, H/J class products offer stronger pressure-bearing capacity and can adapt to frequent load changes in combined cycle systems. Even during unit start-stop or operating condition adjustments, they maintain stable steam parameters, avoiding equipment wear caused by parameter fluctuations. Additionally, the flue gas channel design of H/J class HRSGs is more rational, featuring low flue gas resistance that reduces the backpressure loss of gas turbines, further enhancing the operational efficiency of the entire combined cycle system—making them indispensable core equipment in high-efficiency combined cycle power generation projects.

Key Pressure Control Operations for H/J Class HRSG Boilers During Start-Up and Shutdown Phases

Pressure fluctuations in H/J class HRSG boilers during start-up and shutdown phases easily cause fatigue damage to heating surfaces. Precise operations are required to control the pressure change rate and ensure equipment safety. The start-up phase must follow the principle of “gradual pressure rise”: first, deaerated water is injected into the boiler to the normal water level, and small fires or low-flow flue gas are used for preheating to slowly raise the boiler water temperature to 100-120℃, expelling air from the heating surfaces. Subsequently, the gas turbine load is gradually increased to raise the flue gas temperature, allowing the boiler pressure to rise at a rate of 0.2-0.3MPa/h—preventing uneven expansion of heating surfaces due to sudden pressure surges. When the pressure reaches 30% of the rated pressure, pressure rise is paused for “pressure-stabilized purging.” Drain valves are opened to discharge condensed water from the heating surfaces, preventing water hammer. When continuing to raise the pressure to 80% of the rated pressure, another pressure-stabilized inspection is conducted. Only after confirming that accessories such as safety valves and pressure gauges are functioning normally can the pressure be raised to the rated level. The shutdown phase requires controlling the “pressure reduction rate”: first, reduce the gas turbine load to decrease flue gas input, allowing the boiler pressure to drop at a rate of 0.15-0.25MPa/h—avoiding contraction deformation of heating surfaces due to sudden pressure drops. When the pressure falls below 0.5MPa, open the exhaust valve and drain valve to discharge residual steam and accumulated water in the boiler, preventing low-temperature corrosion. Throughout the start-stop process, parameters such as pressure, temperature, and water level must be monitored in real time to ensure fluctuations are within allowable ranges (pressure fluctuation ≤±0.1MPa, temperature fluctuation ≤±20℃).

Comparative Analysis of Thermal Efficiency Between H/J Class HRSG Boilers and Conventional Boilers

The difference in thermal efficiency between H/J class HRSG boilers and conventional boilers (such as coal-fired boilers and oil-fired boilers) mainly stems from differences in heat sources and recovery methods. In terms of heat utilization efficiency, H/J class HRSG boilers use waste heat discharged by gas turbines as the heat source, eliminating the need for additional fuel consumption. Their thermal efficiency is calculated based on the “waste heat recovery rate,” typically reaching 85%-90%—meaning over 85% of flue gas waste heat is converted into steam energy. In contrast, conventional coal-fired boilers require burning coal and other fuels to generate heat. Their thermal efficiency is affected by fuel combustion efficiency and heat loss, typically ranging from 80%-85%, with additional costs and energy consumption for fuel transportation and storage. In terms of off-design efficiency, H/J class HRSG boilers exhibit a thermal efficiency fluctuation of no more than 5% within the 30%-100% load range, adapting to frequent load adjustments in combined cycle systems. Conventional boilers, however, experience a significant decline in combustion efficiency at low loads (<50%), with thermal efficiency potentially decreasing by 10%-15% and energy consumption increasing markedly. Additionally, H/J class HRSG boilers feature a lower exhaust gas temperature (typically <120℃), resulting in less waste heat loss; conventional boilers generally have an exhaust gas temperature of 150-180℃, leading to more heat waste. Overall, in combined cycle power generation scenarios, H/J class HRSG boilers outperform conventional boilers in both thermal efficiency and economy.

Scaling Cleaning and Corrosion Prevention Strategies for Heating Surfaces of H/J Class HRSG Boilers

The heating surfaces (economizers, superheaters) of H/J class HRSG boilers are prone to scaling and corrosion due to long-term contact with high-temperature flue gas and steam. Scientific measures are required for prevention and cleaning. Scaling cleaning methods should be selected based on scale type: for soft carbonate scale, “chemical cleaning” is applicable—inject dilute hydrochloric acid (5%-8% concentration) and corrosion inhibitors into the boiler, soak for 8-12 hours, then discharge and rinse thoroughly with clean water to remove scale from heating surfaces. For hard sulfate or silicate scale, “high-pressure water jet cleaning” is used, utilizing 20-30MPa high-pressure water jets to impact the scale, avoiding corrosion of heating surfaces caused by chemical cleaning. Corrosion prevention measures must be controlled at the source: first, ensure the feedwater quality meets standards—feedwater hardness <0.03mmol/L and oxygen content <0.05mg/L—preventing impurities in water from depositing on heating surfaces and forming corrosion sources. Second, apply corrosion-resistant coatings (such as ceramic coatings and high-temperature anti-corrosion paints) to the flue gas channels to enhance the corrosion resistance of heating surfaces against flue gas. Third, control the exhaust gas temperature to prevent it from falling below the dew point temperature (typically 90-100℃), avoiding condensation of acidic substances in flue gas on heating surface surfaces and causing low-temperature corrosion. Furthermore, endoscope inspections of heating surfaces should be conducted every 3-6 months to detect early signs of scaling and corrosion, preventing fault escalation.

Adaptation Methods Between H/J Class HRSG Boilers and Combined Cycle Power Generation Systems

H/J class HRSG boilers require precise parameter matching with gas turbines and steam turbines to maximize the overall efficiency of the combined cycle system. First is “parameter adaptation”: the boiler’s steam parameters (pressure, temperature) must align with the design parameters of the steam turbine. For example, if the steam turbine’s rated pressure is 12MPa and temperature is 535℃, the boiler must ensure the output steam parameter deviation does not exceed ±5%—avoiding reduced turbine efficiency due to mismatched steam parameters. Second is “load adaptation”: the boiler’s evaporation capacity must be dynamically adjusted based on the flue gas volume of the gas turbine and the steam consumption of the steam turbine. Devices such as “flue gas dampers” and “bypass flues” are installed to regulate the volume of flue gas entering the boiler when the gas turbine load changes, keeping the boiler’s evaporation capacity balanced with the steam turbine’s demand. For instance, when the gas turbine load increases by 10%, the flue gas damper is opened to increase flue gas flow rate, synchronously increasing the boiler’s evaporation capacity by 8%-10%. Additionally, “control logic adaptation” must be considered: the boiler’s pressure and water level control systems should be linked with those of the gas turbine and steam turbine to achieve “one-click start-stop” and “fault-linked protection.” When the boiler experiences faults such as overpressure or water shortage, the gas turbine load is automatically reduced and the steam turbine inlet valve is closed to prevent accident spread. After adaptation, a “joint commissioning test” is conducted to simulate system operation under different working conditions, ensuring coordinated and stable operation of the boiler and other equipment.

Response Measures and Safety Specifications for Flue Gas Temperature Fluctuations in H/J Class HRSG Boilers

Flue gas temperature of H/J class HRSG boilers is prone to fluctuations due to gas turbine load and fuel composition. Excessively high or low flue gas temperatures affect equipment safety and efficiency, requiring targeted response measures. When flue gas temperature is excessively high (exceeding the design temperature by over 50℃), the gas turbine load must be reduced immediately, and the bypass flue opened to divert part of the high-temperature flue gas.