Questions about oven drying? ?

The original poster didn’t look carefully. . On the first day, the flue gas temperature at the furnace outlet should be below 50°C. . The temperature indicated refers to that at the furnace outlet, as it is difficult to measure the temperature inside the furnace during the heating process. . Therefore, a temperature rise of 20 degrees can be considered as a 20-degree rise in the exhaust gas temperature. . This is used to determine the furnace temperature rise. The 220 degrees mentioned last also refer to the exhaust gas temperature~~~! Furnace flue gas temperature

The smoke temperature in the steering chamber can also be used as a criterion.

1. If there is a superheater, the measurement points for the outlet flue gas temperature should all be located after the economizer. 2. The 20°C mentioned in the requirement that the daily temperature rise should not exceed 20°C refers to the temperature rise of the outlet flue gas. 3. The highest temperature at the end

What is referred to here is the flue gas temperature at the outlet of the boiler furnace, not the exhaust gas temperature. The exhaust gas temperature is not designed to be that high; if it were to reach 200 degrees, how high would then the temperature inside the furnace have to be?

The designed flue gas temperature for boilers generally does not exceed 220°. Since the temperature inside the boiler during operation cannot be measured, only the flue gas temperature can be used as a reference.

The selection of the furnace heating rate is related to the furnace wall structure. The temperature rise is measured at the rear of the boiler. (I think it’s the temperature behind the economizer.) Furnace drying (from “Boiler Operators – Technician Skills”). 1. Purpose of furnace drying: Furnace drying involves heating and baking new boilers that have been just constructed or those that have been out of use for a long time before putting them into operation. This is done to prevent the moist furnace walls from expanding due to the rapid evaporation of moisture when they come into contact with hot flue gases; such expansion can generate pressure, leading to cracks or deformation in the furnace walls, and in severe cases, even to their collapse. When drying the furnace, it should be done slowly so that the moisture in the furnace structure can evaporate gradually; this is necessary to increase the strength of the furnace. 2. Preparatory work before firing the furnace: (1) The boiler and its auxiliary equipment have been fully assembled, subjected to a hydrostatic test, and passed the inspection. (2) The thermal instruments have passed calibration, and the auxiliary equipment such as fans and pumps required for the oven has completed its trial operation and is ready to be put into use at any time. (3) Install the expansion indicators on the boiler drum and header. If the equipment does not have an expansion indicator, a temporary expansion indicator should be installed on the boiler drum and header at a location easily accessible for inspection. (4) After the furnace wall is built, the doors and openings should be opened to allow ventilation and drying for a period of time. (5) Check whether each heating surface tube bank is unobstructed, whether the furnace chamber, flue ducts, and air ducts are clean, and whether any debris in the expansion joints has been removed. (6) For boilers equipped with economizers, the inlet damper of the main flue should be closed and the bypass flue should be used; in the absence of a bypass flue, the outlet of the economizer should be opened to ensure that water is present for cooling inside the economizer. (7) Before filling the boiler with water, open all the exhaust valves and superheater drain valves on the boiler, fill it with treated softened water until the normal water level is reached, and then clean the water level gauge. (8) Select the monitoring (temperature measurement) points for the furnace wall. Unless otherwise specified in the equipment technical documents, the monitoring (temperature measurement) point should be located at the following position: 1) in the middle of the side wall of the combustion chamber, at a height of 1.5 to 2 m above the grate. 2) The middle of the side walls on both sides of the superheater or the corresponding furnace opening. 3) The middle of the smoke arrester or the rear wall of the corresponding flue. (9) Prepare enough firewood and other fuels, and close all doors and openings on the furnace wall. 3. Methods of drying The common methods of drying are three: flame drying, steam drying, and hot air drying. The choice of furnace drying method should be determined based on the actual conditions at the site. Most small boilers use the flame drying method, while larger boilers employ the steam drying method or hot air drying method. The furnace wall is made of concrete, and the firing should take place after the curing period has elapsed. The typical curing times are: about 3 days for alumina cement, and about 7 days for sulphate cement and slag silicate cement. (1) Flame drying: Before starting the drying process, turn on the exhaust fan and blower to remove the gases from the furnace chamber. Start by lighting the fire with wood and ensuring natural ventilation; add coal to the fire as needed, depending on the required baking time and temperature, in order to increase the temperature. To prevent the grate from burning out, it should be rotated regularly. During the first 3 days of heating the furnace, place the wood in the middle of the grate, covering about half of the grate’s surface area, and use a low heat; the fire should not be too close to the walls. The flue damper is opened to 1/6 – 1/5 to allow slow flow of flue gas; the negative pressure in the furnace chamber is maintained at 5 – 10 Pa, and the temperature of the boiler water is kept at 70 – 80°C. After 3 days, a small amount of coal can be added to gradually replace wood for heating; the flue damper should be set at 1/4 to 1/3, ventilation should be increased appropriately, and the temperature of the water in the furnace should reach a level where it boils slightly. The temperature rise during furnace heating should be measured at the rear part of the boiler. Depending on the type of furnace and the structure of its furnace walls, the following rules apply regarding this temperature rise: 1) For furnaces with heavy furnace walls, the temperature rise on the first day should not exceed 50°C; thereafter, it should not exceed 20°C per day. The temperature of the flue gas in later stages should not be higher than 220°C. 2) For lightweight furnace walls, the temperature rise per day should not exceed 80 ℃, and the flue gas temperature at later stages should not be higher than 160 ℃. 3) The furnace wall made of fire-resistant concrete: the temperature rise of the furnace should not exceed 10°C per hour; the temperature of the smoke at later stages should not exceed 160°C, and the furnace should remain at this maximum temperature for no less than 24 hours. If the furnace wall is severely damp, the rate of temperature increase should be reduced appropriately to prevent cracks and deformation in the furnace wall. The selection of the furnace drying time should be determined based on factors such as the boiler’s evaporation capacity, boiler type, furnace wall structure, degree of moisture in the furnace wall, and local climate conditions. The light furnace wall can last 4 to 7 days, while the heavy furnace wall can last 7 to 14 days. (2) Steam drying: Before drying the furnace, fill the boiler with water to the normal level. Connect a steam source to the drain pipe located at the bottom of the water wall collection box, and feed saturated steam at a pressure of 0.3 to 0.4 MPa into the boiler and its economizer. Gradually heat the water inside the boiler until its temperature reaches 90 °C, using this temperature of the boiler water to dry the furnace walls. The normal water level should be maintained in the furnace. When moisture is generated inside the furnace, the dampers and the furnace doors at the upper part of the boiler should be opened to remove the moisture and ensure that all parts of the furnace wall dry out evenly. Drying time for the furnace: For lightweight furnace walls, it is generally 4 to 7 days; for heavy-duty furnace walls, it is usually 14 to 16 days. If the boiler is too humid, flame drying can be used as a supplementary measure later in the drying process. (3) Qualification criteria for oven drying: Once the oven walls have been dried, if there is no deformation, cracking, or any other abnormalities, then the purpose of oven drying has been achieved. The acceptance criteria for furnace drying can be determined in two ways. 1) Furnace wall mortar testing method: At a height of 1.5 to 2 m above the grate in the middle of the furnace walls on both sides of the combustion chamber (1 to 1.5 m above the burner), as well as in the middle of the side walls of the superheater (or at an equivalent position), samples of mortar from the intersections of refractory bricks and red bricks are taken (50 g each), and their moisture content should be less than 2.5%. 2) Temperature measurement method: At a depth of 100 mm inward from the outer surface of the red brick, at a height of 1.5 to 2 m above the grate in the middle of the side walls of the combustion chamber (or 1 to 1.5 m above the burner), the temperature of the furnace wall is measured. This measurement should be maintained at 50°C for 48 hours, or until the temperature at the junction between the refractory bricks and the insulation layer on the side walls of the superheater (at corresponding positions) reaches 100°C, after which it should also be maintained for 48 hours. (4) Precautions during furnace drying: Before drying the furnace, it is necessary to establish a drying curve and operating procedures based on the structure of the boiler, the properties of the refractory materials used, and the season in which the furnace is being built. The precautions for oven drying are as follows: 1) The drying time, rate of temperature rise, time at constant temperature, maximum temperature, etc., must all be followed according to the established drying curve during oven drying, and the actual drying curve should also be measured. The temperature must be strictly controlled to ensure the quality of oven drying. 2) When the furnace reaches a certain temperature and steam is generated, the valves on the boiler drum and superheater headers should be opened to remove the steam promptly. To maintain normal water levels, regular sewage discharge is necessary. 3) During baking, the furnace walls should be checked frequently; their temperature must be controlled. It is advisable to open the viewing ports and other openings as little as possible to prevent cold air from entering the furnace and to avoid cracks in the furnace walls. 4) Heating and cooling in the oven should be carried out slowly; the inlet water temperature should not be too high nor too low (it should be no lower than the ambient temperature).

I’m not sure how to handle small combustion chambers; is there any standard for them? (Hydrogen sulfide combustion chambers)