To ensure the stable operation of steam boilers in the papermaking industry, it is necessary to establish a full-process management system from four dimensions: preparation before operation, control during operation, regular maintenance and upkeep, and formulation of emergency plans. Considering the characteristics of continuous production and large fluctuations in steam demand in the papermaking industry, the specific measures are as follows
I. Before operation: Make basic preparations and calibrate parameters
Precisely match the steam load
The steam consumption in the processes of pulping, cooking, papermaking and drying in the papermaking production line fluctuates greatly. It is necessary to calculate the maximum instantaneous steam consumption and the average steam consumption in advance, and configure steam accumulators to balance peak and off-peak loads, so as to avoid frequent start-up and shutdown of the boiler or overloading operation.
At the same time, ensure that the rated evaporation capacity of the boiler reserves a margin of 10% to 20% to meet the temporary production increase demands of the production line.
Strict control over fuel and water quality
Fuel management: Paper mills commonly use biomass fuels such as black liquor, tree bark, and wood chips. It is necessary to ensure the stability of the fuel’s calorific value and that the moisture content meets the standard (the moisture content of biomass fuel is recommended to be ≤25%) to avoid unstable combustion in the furnace due to fluctuations in fuel calorific value. Black liquor needs to be filtered to remove impurities to prevent clogging of nozzles or grate.
Water quality management: Papermaking boilers have extremely high requirements for the quality of feed water. They need to be equipped with water softening and deaeration devices, strictly controlling the hardness of the feed water to be ≤0.03 mmol/L and the dissolved oxygen to be ≤0.05 mg/L, to prevent scaling and corrosion on the boiler’s heating surfaces, which may affect heat transfer efficiency and equipment lifespan.
Pre-inspection of equipment and systems
Before starting, it is necessary to check whether the safety accessories such as the boiler body, safety valve, pressure gauge and water level gauge are sensitive and reliable. Check the flow conditions of waste heat recovery devices such as economizers and air preheaters; Confirm the valve opening and closing status of the steam network to avoid “blind pipes” or steam leakage.
Ii. During operation: Strengthen real-time monitoring and load regulation
Real-time monitoring of core parameters
Establish a boiler operation monitoring system to track key parameters such as steam pressure, steam temperature, water level, furnace negative pressure, and flue gas temperature in real time. Set parameter fluctuation thresholds (such as steam pressure fluctuation ≤±0.05 MPa), and immediately alarm once the limit is exceeded.
Key focus:
Water level control: A three-stroke water level regulation system is adopted to prevent full water or water shortage accidents.
Combustion control: Automatically adjust the fuel supply volume and the volume of forced and induced draft air according to the load changes to maintain the optimal air-coal ratio, ensure complete combustion in the furnace, and reduce the heat loss of flue gas.
Load regulation suitable for papermaking production lines
The steam consumption of the papermaking production line varies with the pulping batch and the papermaking speed. The boiler needs to have a wide load adjustment capacity (stable operation at 30% to 110% of the rated load).
Intelligent interlocking control can be adopted: The boiler control system can be connected to the DCS system of the papermaking production line. Based on parameters at the steam-consuming end such as the temperature of the drying cylinder and the pressure of the steamer, the combustion conditions of the boiler can be automatically adjusted to achieve precise matching of supply and demand.
Reduce steam loss and recycle it
Regularly inspect the steam pipeline network, promptly repair leakage points, and insulate the pipelines to reduce heat dissipation losses.
The condensate water discharged from the drying cylinder is recovered in a closed manner, and the high-temperature condensate water is directly used as boiler feed water. This not only reduces the cost of soft water preparation but also utilizes the residual heat of the condensate water to increase the boiler feed water temperature and lower fuel consumption.
Iii. Regular Maintenance: Establish a standardized maintenance system
Cleaning and inspection of the heating surface
Descaling: Depending on the water quality, chemical cleaning or mechanical descaling should be carried out on the boiler heating surface every 3 to 6 months to prevent the decline in heat transfer efficiency and local overheating damage caused by scaling.
Ash cleaning: Regularly clean the accumulated ash in the economizer, air preheater and bag filter to ensure smooth flow and reduce flue gas resistance.
Calibration and maintenance of safety accessories and auxiliary equipment
Safety valve: Manual discharge tests are conducted every quarter, and it is sent to a professional institution for calibration every year to ensure the accuracy of the take-off pressure.
Pressure gauges and water level gauges: Calibrated once a month to ensure accurate indication.
For auxiliary machines such as forced and induced draft fans and feed water pumps: Regularly check the bearing temperature and lubricating oil level, and replace worn parts in a timely manner to prevent boiler shutdown due to auxiliary machine failure.
Special maintenance for fuels dedicated to papermaking
If black liquor or high-ash biomass fuel is used, the frequency of cleaning the grate and nozzles should be increased to prevent coking and blockage. Regularly inspect the pipelines and valves of the alkali recovery system to prevent corrosion and leakage.
Iv. Emergency Management: Develop contingency plans and conduct regular drills
Establish emergency response plans for common faults
In response to common faults in papermaking boilers such as sudden drops in steam pressure, coking inside the furnace, and interruption of water supply, detailed emergency procedures have been formulated, clearly defining the handling steps for operators, for example:
When the steam pressure drops sharply, priority should be given to ensuring the steam supply for the papermaking and drying process, and the load of the pulping process should be temporarily reduced.
When coking occurs in the furnace, the combustion conditions should be adjusted in a timely manner, and mechanical decoking or manual cleaning should be adopted after the furnace is shut down.
Regularly carry out emergency drills
Organize a boiler malfunction emergency drill every six months to test the handling capabilities of the operators and at the same time improve the loopholes in the contingency plan.
Reserve key spare parts
Stock up on key spare parts such as safety valves, pressure gauges, nozzles and pump impellers in advance to avoid prolonged downtime due to shortage of spare parts.