(1) Technical scope of application

Heating furnaces are used in many industries such as petroleum, chemical industry, metallurgy, machinery, heat treatment, surface treatment, building materials, electronics, materials, light industry, daily chemical, pharmaceuticals, etc., and are mainly used to heat materials or workpieces (usually metals) to rolling to the forging temperature.

(2) Technical principles (transformation content)

① Technical introduction

Liquid (gaseous) fuel burns in the radiant chamber (furnace) of the heating furnace, producing high-temperature flue gas and using it as a heat carrier, flowing to the convection chamber and discharged from the chimney. The raw acCGAMF oil to be heated first enters the convection chamber tubes of the heating furnace, and the crude oil temperature is generally 29℃. The furnace tube mainly obtains heat from the flue gas flowing through the convection chamber through convection, and this heat is transferred from the outer surface of the furnace tube to the inner surface of the furnace tube through heat transfer, and at the same time, it is transferred to the crude oil flowing in the tube through convection. Crude oil enters the radiation chamber tubes from the convection chamber tubes. In the radiation chamber, the flame sprayed from the burner mainly radiates part of the heat to the outer surface of the furnace tube in a radiating manner, and the other part radiates to the furnace wall on which the furnace tube is laid. The furnace wall radiates heat to the outer surface of the furnace tube on the side of the fire back surface in a radiating manner. These two parts of radiant heat work together to raise the temperature of the outer surface of the furnace tube and form a temperature difference with the inner surface of the tube wall. The heat flows to the inner wall of the tube by conduction, and the crude oil flowing in the tube continuously obtains heat from the inner wall of the tube by convection, realizing the process requirements for heating crude oil.

The heating capacity of the heating furnace depends on the intensity of the flame (furnace temperature), the surface area of the furnace tube and the total heat transfer coefficient. The stronger the flame, the higher the furnace temperature, the greater the temperature difference between the furnace and the oil flow, and the greater the heat transfer amount; the larger the area of the furnace tube where the flame and the flue gas contact, the more heat transfer amount; The better the heat transfer performance of the furnace tube., the more reasonable the furnace structure, the more heat transfer amount. The strength of the flame can be adjusted by controlling the nozzle. However, for furnaces of a certain structure, the furnace temperature will no longer rise after reaching a certain value under normal operating conditions. The total heat transfer coefficient on the surface of the furnace tube is certain for a furnace, so the heating capacity of each furnace has a certain range. In actual use, poor flame burning and coking of the furnace tubes will affect the heating capacity of the furnace. Therefore, attention should be paid to controlling the burner to make it burn completely, and to prevent coking caused by excessive temperature of the local furnace tubes.

② Energy saving principles

The level of thermal efficiency determines the productivity of the heating furnace. With the increase of productivity, as the consumption of steel and coal decreases, gas is saved and costs are reduced. First of all, the heat carried away by waste gas must be reduced. The purer the gas produced by the gas furnace, the more waste gas will be. Less, less heat is taken away in the furnace, improving the thermal efficiency.

The main components of gas are C0, H2 and various CH compounds:

C+02+H20-H2+CO+C02

C02+C--CO+C02

CO+02-C02

S+02--S02

Among them: SO2 is exhaust gas, so high-quality coal must be selected when selecting coal. The utilization of waste heat requires the vaporized and cooled steam and water mixture to be collected into the steam drum. First, it can be supplied to the canteen, and then it can be supplied to the heating of the bathhouse and family area. The utilization of heat energy is increased, so energy is saved and costs are reduced.

G=(Q*A-Q loss)/△i G hourly output. Q Heat supply, heat utilization rate, fuel utilization coefficient 0 is the heat lost △i is the heat required per unit of steel.

Reduce the heat from cooling water and heat the water pipes and door at the bottom of the furnace. The furnace carries away a considerable amount of heat, so the water pipes at the bottom of the furnace must be wrapped with insulation materials to reduce the loss of heat. Reduce heat loss from the furnace body, mainly including: heat loss such as water cooled furnace door radiation, gas escape, and heat loss from the lining. Reducing this heat can greatly reduce unit consumption. The tower must be sealed in time for the half-fire of the burner in Zhou Guo, and the gas leakage from the small door on the furnace body must be eliminated. The medium gas pipeline must be frequently inspected and sent in time to reduce heat loss, improve heat utilization, increase fuel utilization coefficient, reduce the heat required per unit of steel failure, and all can improve thermal efficiency and increase hourly output.

With a good process operation system, computer control, and low fuel ratio combustion instructions, the heating furnace must be correctly operated according to regulations to ensure heating quality, and daily inspections of each major process system of the heating furnace must be carried out. According to the heating temperature requirements, observe the flue gas at the end of the furnace and adjust the fan frequency with the color of the beginning of the fire. Adjust the mixing ratio of medium gas and air. Frequent observation, work connection, and adjustment must be carried out, and frequent observation must be made to see whether the flame in the furnace is bright, the length of the flame, the size of the air volume, and the uniformity of the steel in the furnace to prevent the burner from breaking off and tempering. If the fire is cut off, the air volume of the burner must be reduced, and the air volume in front of the burner must be increased after tempering to ensure uniform combustion after the flame is sprayed out. The application of new processes and new materials and the damaged hot charging and hot delivery have a great impact on heating costs. Therefore, the improvement of thermal efficiency is also crucial to the energy conservation of the heating furnace.

(3) Application cases

Baoshan Iron and Steel Co., Ltd. Baoshan Steel Wire Rod Heating Furnace Energy Saving Transformation Project.

(1) Brief description of the basic situation: Baoshan Iron and Steel Co., Ltd. is a listed subsidiary and the main unit of steel production and operation of Baowu Group Co., Ltd., and its industry is ferrous metal smelting and rolling processing. Due to the low return water temperature of the water cooling system, the heat carried away by the cooling water cannot be effectively utilized; the temperature of the smoke entering the air preheater is about 580 ° C, and the air is preheated to 350 ° C ~420 ° C, and the temperature of the discharged smoke is about 320 ° C. The waste heat utilization rate is low; The original design water beam column wall thickness is 16.0mm, and the technical requirements are that when the water beam column wall thickness is ≤12.0mm, it is necessary to plan and arrange replacement; when the water beam column wall thickness is ≤8.0mm, it cannot be used. In February 2015, one column leaked (it had been in operation for 16 years) and was replaced during major maintenance in May 2015 (at the same time, two other columns in the same circuit were replaced); during the scheduled maintenance, the wall thickness of the water beam column was measured, which was basically between 11.4mm and 13.6mm; the walking beam deviated in the longitudinal and horizontal directions; the deviation between the discharge center line of the heating furnace and the rolling center line was large; the flow switch of the water beam column was easily blocked;

Problems such as aging of furnace body refractory materials and aging of burner bricks; poor linearity of gas and air system flow control valves at low flow rates.

(2) Implementation content and cycle: ① Due to the change in cooling method of the water beam column, and considering that the service life of the heating furnace has been nearly 18 years, most of the water beam columns and cushion blocks are seriously corroded or worn, this renovation is all updated;② The translation frame remains unchanged, but the position connected to the movable column is improved accordingly to improve the running stability of the walking beam; improve the alignment between the center line of the tapping roller table in the furnace and the rolling center line;③ All water sealing grooves and slag scraping mechanisms are replaced; ④ The steel structure of the furnace bottom remains unchanged, but the position connected to the fixed column is made of welded section steel and steel plates and fixed with bolts, and needs to be treated accordingly; ④ All furnace bottom refractories are demolished and built; ④ End walls, side walls and furnace top refractory materials are all demolished and built; ③ Due to the decrease in flue gas temperature and the increase in flue gas resistance, the existing chimney has insufficient pumping force, and a new smoke exhaust fan has been added. The implementation cycle is 16 months.

(3) Energy conservation and emission reduction effect and investment payback period: The annual standard coal saved after the transformation is 4889 tons, and the annual saving is 12.22 million yuan based on the price of 2500 yuan/ton. Therefore, the static investment payback period is approximately: 2748.64 / 1222 =2.25 (years), that is, the investment payback period is approximately 2 years and 3 months.

(4) Potential for replication and promotion, energy-saving potential (payback period)

This technology is widely used in the steel industry and is used for energy-saving technical transformation of heating billets, rolling, etc. The technical transformation method is safe and reliable, can effectively improve the shortcomings of existing heating furnaces, has great energy conservation potential, and has obvious energy conservation and emission reduction effects., broad prospects for promotion and application, and great potential for replication.