Rotary furnace with external heat exchange devices

Abstract

This utility model relates to the construction materials industry, specifically to technology for burning Portland cement clinker and producing lime in a rotary kiln with external heat exchangers. The rotary kiln consists of a housing 1, the inner surface of which is lined with refractory brick. External heat exchangers 9 are arranged uniformly around the periphery of the housing 1, connected to the interior of the housing 1 through openings therein. In the proposed solution, external heat exchangers 9 are located in the decarbonization zone and are made of steel, in the form of a spherical volume. The technical result consists in creating a rotary kiln with external heat exchangers, characterized by improved heat exchange between the gas flow and the fired material. 2 fig.

Description

[0001] The utility model relates to the building materials industry, in particular to the technology of the process of firing Portland cement clinker and producing lime in a rotary kiln with external heat exchange devices.

[0002] A known design of a rotary calcining kiln [US Patent No. 3,271,018, "Rotary Calcining Kiln," published September 6, 1966] consists of a housing with open ends, mounted for rotation on bearings at an angle, lined with refractory bricks, heat entering from a burner, and material entering through a chute from the cold end of the kiln. External heat exchangers, in the form of an inverted truncated square pyramid, are located along the surface of the kiln housing and fixed to it by means of a flange connection. These heat exchangers are made of metal or ceramic material and have a detachable connection.

[0003] The disadvantage of the rotary kiln is the slow loading and unloading of the material due to the narrow lower part of the heat exchange devices, which leads to deterioration of the heat exchange of the material with the exhaust gases and the heat exchange surface.

[0004] A known design of external heat exchange devices for rotary kilns and the like is [US Patent No. 3,782,891A, "External Material Lifters for Rotary Kilns and the Like," published January 1, 1974]. The device consists of a casing located at an angle, which rests on tires and support rollers; heat is supplied to the casing by a burner, and the material is supplied through a chute from the cold end of the kiln casing. External heat exchange devices are located around the periphery of the casing, in the form of a hollow cylinder connected by a parallelepiped parallel to the axis of the heat exchanger cylinder and at an angle relative to the axis of the kiln. These devices are welded to the casing with openings and rotate with it along a circumference, and allow a portion of the material to be lifted from the casing bottom to ensure mixing of the material over the entire diameter of the casing.

[0005] The disadvantages of rotary kilns and similar equipment include a smaller heat exchange surface area between the material and the heat exchanger compared to other heat exchangers of the same volume. Suboptimal material distribution in the gas flow, caused by the design of the heat exchangers, reduces heat transfer.

[0006] The closest technical solution selected as a prototype is improved rotary kilns and related technologies [GB Invention No. 343513A "Improvements in and relating to rotary kilns", February 18, 1931]. The rotary kiln consists of a lined casing with external heat exchangers mounted on the outside, connected to its interior through openings. The heat exchangers are positioned at an angle to the longitudinal axis of the kiln casing and are evenly distributed throughout the casing. They are installed in three sections of the kiln, along the longitudinal axis of the kiln. The heat exchangers are cylindrical and welded to the casing through rectangular boxes, which are lined on the inside with refractory.

[0007] The following set of features of the prototype coincide with the essential features of the claimed utility model: a housing, the inner surface of which is lined with fireproof brick, and on the outside of the housing, external heat exchange devices are evenly located along the periphery, connected to the inner part of the housing through openings made in it.

[0008] The disadvantage of the prototype is a significant decrease in the strength of the housing, stagnant zones, since the material sticks in the boxes and remains inside longer than the required residence time, which worsens heat exchange and the quality of the finished product.

[0009] The utility model is aimed at creating a rotary kiln with external heat exchange devices, characterized by improved heat exchange between the gas flow and the fired material.

[0010] This is achieved by a rotary kiln consisting of a housing, the inner surface of which is lined with refractory brick. External heat exchangers are arranged evenly around the periphery of the housing, connected to the interior of the housing through openings. In the proposed solution, the external heat exchangers are located in the decarbonization zone and are made of steel, in the form of volume of the sphere.

[0011] The essence of the utility model is explained by drawings, where Fig. 1 shows a rotary kiln with external heat exchange devices (main view), Fig. 2 is a section A-A in Fig. 1 of the housing with external heat exchange devices, Fig. 3 shows the arrangement of external heat exchange devices on the development of the housing of a rotary kiln with external heat exchange devices.

[0012] A rotary kiln with external heat exchange devices consists of a housing 1 welded from shells 2 made of steel, supported by bandages 3 on support rollers 4. The rotary kiln has a drive, which consists of an electric motor 5, a gearbox 6, a crown gear 7 and a crown gear 8 fixed to the housing 1. External heat exchange devices 9 are made in the form volume of the sphere. External heat exchange devices 9 are arranged uniformly on the outside along the periphery of the housing 1 and are connected to its interior through openings made in the housing. External heat exchange devices 9 are made of steel. Along the length of the housing 1, heat exchange devices 9 are arranged in the decarbonization zone, namely, through two shells from the ring gear 8, in the direction of movement of the material secured to the housing 1, namely, on the third, and then through one shell 2, namely, on the fifth shell 2. In this case, the inner surface of the housing is lined with refractory brick 10.

[0013] The operating principle of a rotary kiln with external heat exchange devices is considered using the clinker firing process.

[0014] The furnace is rotated by an electric motor 5 through a gearbox 6, a crown gear 7 and a crown gear 8 fixed to the body 1. The material, for example, sludge, is fed from the loading end (not shown in the figure) into the body 1, which rests on the bandages 3 and support rollers 4, and the flow of hot gases is fed through the burner device (not shown in the figure), from the discharge end of the furnace (not shown in the figure). Gradually, the material moves along the body 1 due to the tilt of the furnace, and in the decarbonization zone, the material enters through the openings in the body 1 into the external heat exchange devices 9, which are located outside the body 1.

[0015] Case 1 and external heat exchangers 9 are made of steel, which has high thermal conductivity, enabling heat transfer from the hot gas flow within case 1 to the external heat exchangers 9 heated by these gases. Coating may form in the area where the external heat exchangers are installed. Therefore, if the external heat exchangers are lined, they may become coated with coating and cease to perform heat transfer. If the external heat exchangers are constructed solely of steel, which has a different coefficient of thermal expansion than the coating, coating will not form on their surface. Any coating that adheres during operation will fall off, as the attachment point will fail due to stresses arising during the heating-cooling cycle, due to the large difference in the thermal expansion coefficients of the materials.

[0016] When the material enters the external heat exchange devices 9, heat is transferred to the material, ensuring improved heat exchange between the gas flow and the fired material. The heated material then returns to the housing 1.

[0017] The inner surface of body 1 is lined with refractory brick 10, which has low thermal conductivity, reducing heat loss through the furnace walls and improving heat exchange. Due to the fact that external heat exchangers 9 are located in the decarbonization zone, namely, two shells 2 away from ring gear 8, namely on the third, and one shell 2 away from it, namely on the fifth shell 2, this arrangement promotes a more uniform temperature distribution along the length of the furnace, which improves material decarbonization, and accordingly improves heat exchange and reduces the load on body 1.

[0018] The material then moves along body 1 and enters the discharge end of the furnace, where the finished product is released.

[0019] During numerical simulation, it was found that it is optimal to implement external heat exchange devices in the form of volume of the sphere ( (Fig. 2)), this shape allows for an increase in the heat exchange area and the elimination of stagnant zones within the heat exchange device. Moreover, if the volume of the ball is larger , then the material does not enter the ball sufficiently and heat exchange decreases, and if less , then the fired material exits the external heat exchange devices faster and the heat exchange area is reduced.

[0020] A comparison of the material flow kinematics of the prototype and the proposed device revealed that in the prototype, the material enters the heat exchanger through a rectangular nozzle, which impedes the timely exit of the heat exchanger. As a result, some of the material remains in the heat exchanger, while the rest passes through the rotary kiln body. This disrupts heat exchange between the gas flow and the material being fired, reducing the quality of the finished product.

[0021] In the proposed device, the material is evenly distributed throughout the body and heat exchangers, ensuring its free entry and exit. This facilitates the free passage of gas between the material particles. This improves heat exchange between the gas flow and the fired material, improving the quality of the finished product.

[0022] The proposed solution of external heat exchange devices can improve heat exchange between the gas flow and the fired material.

Claims

A rotary kiln with external heat exchange devices, consisting of a housing, the inner surface of which is lined with firebrick, and on the outside of the housing, external heat exchange devices are evenly distributed around the periphery, connected to the inner part of the housing through openings made in it, characterized in that the external heat exchange devices are located in the decarbonization zone, made of steel, in the form volume of the sphere.

Images