Boilers are the most commonly used industrial equipment and have a wide range of applications in all industries. EPCB has also made qualitative breakthroughs in boiler technology research, effectively solving some boiler operation problems and ensuring the safety and efficiency of boilers.

This paper briefly introduces the boiler, introduces its structure, and proposes the adjustment technology in daily operation, which has an important guiding role in reducing energy consumption and improving the efficiency of boiler operation.

As far as industrial boilers are concerned, in order to improve boiler efficiency:

1. Minimize various losses by adjusting the operation mode;

2. Eliminate defects and problems that affect economy through maintenance;

3. Improve steam parameters and reduce the amount of desuperheating water and sewage.

Among all the losses, exhaust heat loss and mechanical incomplete combustion heat loss are the main ones, so effectively reducing these losses can improve boiler efficiency.

What are the factors that affect boiler operation?

The main factors affecting the exhaust heat loss are exhaust temperature and exhaust volume.

Generally speaking, for every 10°C increase in the exhaust gas temperature, the exhaust heat loss increases by 0.6% to 1%. The amount of smoke exhaust is mainly determined by the excess air coefficient and the moisture in the fuel, and the moisture in the fuel is determined by the composition of the coal entering the furnace.

The main factors that affect the exhaust temperature and exhaust volume:

Air leakage.

Air leakage refers to furnace air leakage, pulverizing system air leakage and flue air leakage. Air leakage directly leads to an increase in exhaust heat loss. Practice has proved that for every 0.1 increase in the furnace air leakage coefficient, the exhaust temperature will increase by 3~8°C, and the exhaust heat loss will increase by 0.2%~0.4%.

1) Air leakage in the furnace. Among all the air leakages, the air leakage at the bottom of the furnace has the greatest impact. When the water seal at the bottom of the furnace is lost or the furnace bottom is broken by a large coke, a large amount of cold air will leak from the bottom of the furnace, which will seriously affect the economy and efficiency of the boiler. safe operation;

2) Air leakage in the milling system. The air leakage of the pulverizing system is mainly from the coal and powder pipes. Part of it leaked from the milling system in operation, and another part leaked from the out-of-service milling system, which was mainly due to the fact that the tertiary damper was not completely closed;

3) Air leakage from the flue. When the amount of oxygen remains unchanged, the air leakage of the flue will also displace the primary and secondary air volume, so that the exhaust gas temperature rises. Another hazard of air leakage from the flue is that the cold air leaking into the flue does not participate in the combustion. Since the oxygen meter is installed at the flue gas inlet of the air preheater, the air leakage from the rear flue will make the displayed value of the oxygen content larger than the actual value. It may cause insufficient combustion air volume in actual operation, resulting in oxygen-deficient combustion in the furnace.

Ash and slagging on the heated area.

The problem of local coking at high load in the furnace still exists. Although the boiler adopts a large number of anti-slagging designs, the phenomenon of local coking still exists under high load conditions, which once caused the passive operation of the slagging system and affected the safe and economical operation of the unit.

The ash and slagging of the heated area mainly include ash blocking in the air preheater, ash accumulation in the furnace and flue, etc.

1) The air preheater is blocked by dust;

2) Ash and slagging in the furnace and flue.

The ash accumulation in the furnace and flue will reduce the heat absorbed by the steam from the high-temperature flue gas, thereby increasing the flue gas temperature at the inlet of the air preheater, increasing the heat transfer temperature difference of the air preheater, and increasing the exhaust gas temperature. During the operation of the boiler, there is a serious problem of slagging in the furnace.

During the operation, the slagging directly affects the normal flow state of the air flow and the combustion process in the furnace, and sometimes even causes the boiler to flame out, which affects the safety, economical operation and reliability of the boiler. have a great impact. Since the slagging is often uneven, the slagging of the furnace increases the heat transfer resistance of the water-cooled wall, the water-cooled wall absorbs insufficient heat, and the output of the boiler is reduced, which has an adverse effect on the safety of the boiler's water cycle.

How do I optimize my boiler?

Improve coal quality.

The boiler efficiency is closely related to the coal type. When the volatile moisture content in the fuel is high, the pulverized coal is easy to catch fire, the combustion process is stable, and the heat loss of incomplete combustion is also small, but the probability of coking is increased. When the ash content in the fuel is high, the combustion stability is poor, and because of the insulating effect of the ash, the coal's ember combustion is poor. The effect of moisture on combustion is mainly to make it difficult to burn and reduce the temperature of the combustion zone, making it difficult to burn pulverized coal. Coal quality is the biggest factor affecting the exhaust gas temperature. Store different types of incoming coal separately, do a good job in coal quality analysis, and find out the best coal blending plan. Coal workers must strictly and accurately blend coal according to the specified coal quality requirements.

Reasonably control the amount of oxygen.

When the oxygen content of the boiler furnace outlet of the power plant changes, other main operating economic indicators such as the unburned carbon content of the ash and slag, the exhaust gas temperature, the total power consumption of the induced draft fan, the main steam temperature and the amount of desuperheating water will all change, and the furnace will change. The oxygen output at the outlet is one of the parameters that is easiest to adjust, has the widest variation range, has the strongest coupling with other operating indicators, and has the greatest impact on economy during the operation of the unit.

When the operating oxygen content changes, the most direct impact on the economy comes from the change in the heat loss of the exhaust gas caused by the flue gas volume. At the same time, it will also cause changes in other operating parameters, including: ash and slag unburned ember carbon content , exhaust gas temperature, total power consumption of induced draft fan, main steam temperature and desuperheating water volume and desuperheating water volume. The net effect of variable oxygen operation on the economy of the whole unit is the result of the combined effect of all the above parameters.

At present, most of the oxygen control parameters specified for on-site operation are for the rated load, and are generally selected based on experience based on the type of coal used in the boiler. When the unit is operating at low load peak regulation, the oxygen control is more arbitrary.

Improve the application technology of operators.

Operators should keep abreast of changes in coal types entering the furnace, and adjust the operation of the pulverizing system accordingly according to the coal quality analysis report to ensure proper pulverized coal fineness. Tests can be carried out on the types of coal that are often burned. Do not blindly pursue too low fineness of pulverized coal, and comprehensively consider the power consumption of pulverizing. Strengthen the procurement and storage management of raw coal, control the quality of incoming coal acceptance, strengthen coal yard management, store different types of coal in separate piles, and try to do a good job of mixing coal when the boiler coal hopper is fed, and strictly implement it. Control the moisture of pulverized coal.

Boiler operators should always observe the ignition of pulverized coal, and control the ignition distance of pulverized coal to be about 200-300 mm from the outlet of the primary air nozzle. Adjust the opening of the primary damper in time according to the ignition and tempering of the pulverized coal. The opening of the primary air door does not have to be fully opened, and the opening of the air door can be adjusted according to the wind speed. Do not adjust by adjusting the air pressure only by adjusting the opening of the secondary air door. In normal operation, appropriately reducing the primary air pressure and increasing the primary air temperature will advance the ignition point.

Operators should adjust the combustion in the furnace under high and low load conditions, adjust the ratio of primary air and secondary air, ensure that the furnace flame is not skewed, and ensure a good blend of pulverized coal and air. The mixing characteristics of the primary and secondary air are also an important factor affecting ignition and combustion. If the secondary air is delivered too early, the ignition point will be delayed, but if the secondary air is delivered too late, it will cause oxygen deficiency in the combustion after ignition.

Further strengthen technical supervision and overhaul and maintenance work.

Establish an effective maintenance quality assurance system, and strictly control the maintenance quality at every level, especially to ensure that the equipment defects affecting the performance of the milling system are fundamentally treated during the equipment overhaul.

Strengthen maintenance management and eliminate equipment defects in a timely and rapid manner.

The quality of steel balls is regularly inspected, and acceptance is carried out in strict accordance with the relevant provisions such as wear resistance and impact toughness to ensure the coal grinding capacity and reduce the consumption of steel balls.

Taking the opportunity of boiler maintenance, replace the bluff body in the primary air nozzle that is seriously worn or fallen off; trim and correct the burner nozzle that is burnt, deformed and skewed in time to prevent coal at the primary air nozzle of the burner. The uneven distribution of pulverized coal and the deflection of the pulverized coal flame cause local coking in the furnace and an increase in the exhaust gas temperature.

Through the cold aerodynamic field test of the boiler before the start of the unit, the reasonable air distribution mode of the burner is found out, so that a good aerodynamic working condition is organized in the furnace, and the safe, stable and economical operation of the boiler is ensured.

During the maintenance, the ash and slag removal of each heating surface of the boiler was carried out, the ash pollution degree of the heating surface was reduced, the heat transfer coefficient of the heating surface was increased, and the heat exchange was strengthened, so that the heat absorption of each heating surface reached or approached the design value.

During the overhaul, the tubular air preheater was thoroughly cleaned and plugged.

Conclusion:

All in all, in order to ensure the stable improvement of the operating efficiency of the boiler, it is not only necessary to manage it based on advanced technology, but also to select reasonable fuel for it, to achieve the stability of the air distribution work, and to control the air coefficient to ensure that under the reasonable control of each situation, It can promote the efficient operation of the boiler, and can also improve the operation efficiency of the boiler, so as to obtain effective economic and social benefits as a whole.

Further Reading:

Boiler Guidance----Acceptance After Boiler Installation

Industrial Boiler Low Load Operation Hazards,Causes and Solutions

Thermal Oil Boiler Safety and Energy Saving |Thermal Oil Boiler Scaling Causes, Hazards and Solutions