I. Technology Positioning and Core Parameters

Ultra-supercritical units are cutting-edge technologies in the thermal power generation field. Their boiler systems typically operate at main steam pressures of 25-31 MPa and temperatures of 580-610°C, achieving power generation efficiencies exceeding 41%. For example, the 1000MW unit at the Huaneng Yuhuan Power Plant utilizes an internal separator start-up system equipped with a parallel recirculation pump for efficient recovery of working fluid and heat. The use of core materials such as Super304H steel improves the creep resistance of the heating surface by 30%, supporting the unit's advancement toward 620°C performance levels.

2. Innovations in Startup System Architecture

1. Internal Separator-Driven Design
Unlike traditional drum boilers, ultra-supercritical boilers utilize a once-through circulation system. Start-up systems are categorized as either internal or external. Built-in separators are the mainstream choice due to their simplified system and easy operation.

Structural Features: The separator is integrated between the evaporator and superheater, withstands full-pressure conditions, and requires construction of high-strength alloy steel such as SA-335P92.
Function: Through a water storage tank and a recirculation pump, the separator maintains a water-wall mass flow rate of ≥800 kg/(m²·s) below 30% of rated load, preventing deterioration in heat transfer.
A typical example: The tandem start-up system designed by Shanghai Boiler Plant for the Jiangsu Ligang Project, equipped with an F-60 recirculation pump, achieved a 15% improvement in working fluid circulation efficiency during startup.
2. Breakthrough in Drain Recovery Technology
To address working fluid losses during startup, modern units utilize a three-stage recovery system:

Primary Recovery: Separator drain flows through the water storage tank to the recirculation pump, where it mixes with feed water and returns to the economizer.
Secondary Recovery: Excess drain is depressurized by an atmospheric expansion tank, and the condensate is then returned to the condenser via a drain pump. Tertiary Recovery: High-temperature drain water is introduced into the deaerator, achieving cascaded heat utilization.

Harbin Electric Power Group innovatively applied a T-shaped heating surface layout in its Binchang 660MW CFB project, combined with an internal separator, reducing startup time to 40 minutes, a 25% reduction compared to conventional designs.

3. Key Points for Startup Process Control

1. Cold Cleaning Phase
A two-stage circulating cleaning process using deoxygenated water is performed:

Low-pressure cleaning: Removes impurities from the system upstream of the feedwater pump, reducing the Fe ion concentration to below 50μg/L.

High-pressure cleaning: Hot cleaning is performed at 200°C to ensure that the water quality at the economizer inlet meets standards.

Dongfang Boiler discovered during the commissioning of a 1000MW unit that optimizing the cleaning pump flow curve increased cleaning efficiency by 40% and saved 1,200 tons of water.

2. Ignition Expansion Control
Fuel expansion is a key issue during the initial startup phase:

Fuel Injection Strategy: Utilize a stepped load ramp-up curve, with the initial fuel level controlled at 20% of the MCR to avoid a sudden increase in the steam production point. Water Level Control Technology: The separator water level is controlled via the AN/ANB dual-valve linkage, maintaining a ±0.5m fluctuation range during peak expansion.

The Huaneng Ruijin Power Plant has demonstrated that the implementation of an intelligent expansion prediction model has reduced water level overruns by 70%, and unit startup reliability has reached 99.2%.

3. Dry-Wet Transition Control
When the load reaches 30% ECR, the unit enters dry operation:

Intermediate Point Temperature Control: Maintains the separator outlet superheat at 5-15°C, serving as a feedforward signal for water-coal ratio adjustment.

Sliding Pressure Operation Strategy: Utilizes a "fixed-sliding-fixed" mode to maintain a linear relationship between main steam pressure and load in the 30-95% load range.

The Siemens SPPA-T3000 control system, used in a project, has demonstrated that sliding pressure operation can reduce heat rate by 1.2% and NOx emissions by 15%.

4. Progress in the Localization of Key Equipment

1. Recirculation Pump Technology Breakthrough
The 1000MW-class canned motor pump manufactured in Deyang achieves three major innovations:

Magnetic drive technology: Eliminates the risk of leakage from traditional mechanical seals, increasing MTBF to 8,000 hours.

Variable frequency control strategy: Utilizes a vector control algorithm to achieve stepless flow adjustment from 0-100%.

Material upgrade: The rotor utilizes M35N high-nitrogen stainless steel, improving corrosion resistance by three times.

2. Burner Optimization
To address the challenges of utilizing low-calorific-value coal, a new low-nitrogen burner has been developed:

Dense-lean separation technology: A louvered separator achieves a 3:1 pulverized coal concentration ratio, reducing the ignition temperature by 100°C.

Combustion stabilization ring structure: A swirl combustion stabilization ring is installed at the burner outlet, improving the flame stability index by 40%.

Harbin Boiler applied this technology in the retrofit of a 660MW unit, reducing the fly ash carbon content from 8% to 3% and increasing boiler efficiency by 1.5 percentage points.

5. Operational Optimization Practices

1. Dynamic Stress Monitoring System
Applying fiber Bragg grating sensing technology, we achieve:

Real-time reconstruction of the water-wall temperature field: Monitoring point density reaches 50/m², and temperature deviation is controlled within ±5°C.
Life Assessment Model: A fatigue life prediction system based on the rainflow counting method is established, extending component maintenance cycles by 30%.
2. Intelligent Sootblowing Optimization
Developing a neural network-based sootblowing strategy:

Fouling Deposition Prediction: Analyzing historical data using an LSTM network allows prediction of soot accumulation locations 48 hours in advance.
Sootblowing Timing Optimization: An economic evaluation model is established, reducing sootblowing steam consumption by 25% and flue gas temperature by 3°C.

6. Technological Development Trends

Parameter Improvement: The development of 700°C ultra-supercritical units is accelerating, and the proportion of nickel-based alloy materials used will reach 60%.
Deep Peak Shaving: A startup system capable of 20% rated load is developed to meet the needs of renewable energy consumption.
Digital Twin: A digital model of the boiler's entire lifecycle is constructed to enable virtual commissioning of the startup process. my country has developed a comprehensive ultra-supercritical boiler technology system, reaching internationally advanced levels from material research and development to system integration. As the "dual carbon" goals advance, this technology will play a greater role in the flexibility and efficient utilization of coal-fired power.