Waste heat recovery method and waste heat recovery system

Abstract

The molding sand is placed in tanks (1.1., 1.2.) equipped with tubular heat exchangers (2.1., 2.2.), and the heat from the molding sand is removed in two stages by means of water contained in tubular heat exchangers (2.1., 2.2.) connected to recirculation tanks (3.1., 3.2.) and is stored as water heated to a temperature of up to 90°C in a thermally insulated buffer tank (7), with the first stage reducing the temperature of the molding compound from about 400 to about 200°C and obtaining water at a temperature of not less than 60°C, and the second stage from about 200 to 60-40°C and obtaining water at a temperature of not less than 40°C. The system for waste heat recovery consists of at least two moulding sand cooling modules, where each module contains a moulding sand tank (1.1., 1.2.) equipped with a tubular heat exchanger (2.1., 2.2.) and a recirculation tank (3.1., 3.2.), connected by piping to the circuit of the plate heat exchanger (5) and the emergency cooler (6) and the water buffer tank (7).

Description

[0001] The subject of the invention is a new method for the recovery of technological waste heat, generated in the process of casting massive castings made of metal alloys in sand molds, and a system for the recovery of waste heat.

[0002] In the process of casting massive castings, made of metal alloys, a very large amount of energy is consumed, which is necessary to prepare a melt of liquid alloy with a sufficiently large mass. Once the casting mold is flooded with the liquid alloy, the process of solidification and cooling of the casting begins. During this time, the thermal energy of the liquid alloy is transferred to the casting mold, made of molding compound, the main component of which is quartz sand. Due to the low thermal conductivity of the molding sand, the thermal energy taken over from the casting is accumulated in the inner zone of the mold so that a negligible part of it enters the environment. The mold is opened when the casting reaches a temperature of 400 - 450° C, measured at its surface. The same temperature is reached by the molding compound in the layers adjacent to the casting. As a result of the thermal energy from the cooling casting on the molding mass, it undergoes thermal degradation. The bonds between the grains are destroyed and the mold disintegrates, taking the form of heated sand. In order for the sand to be reused in production, it is cooled to a temperature of about 30° C, and its thermal energy is dissipated into the environment and lost.

[0003] The purpose of the invention is to develop a way to efficiently capture and use the heat energy generated by cooling the casting in other areas of the foundry, such as office space.

[0004] The essence of the invention with respect to the method is that the molding compound is placed in tanks equipped with tubular heat exchangers, and the heat from the molding compound is taken away in two stages by means of water contained in tubular heat exchangers connected to recirculation tanks and stored as water heated to a temperature of up to 90°C in a thermally insulated buffer tank, with the first stage reducing the temperature of the molding compound from about 400 to about 200 °C and obtaining water heated to a temperature of not less than 60 °C, and the second stage from about 200 to 60-40 °C and obtaining water with a temperature of not less than 40 °C.

[0005] Advantageously, the heated water contained in the tubular heat exchangers is sent through pipes to recirculation tanks.

[0006] Advantageously, heated water from the first recirculation tank connected to the heat exchanger of the first molding sand tank is sent through piping to the main water buffer, and lower temperature water from the heat exchanger of the second molding sand tank is sent through piping to the first recirculation tank and mixed there with higher temperature water coming from the heat exchanger of the first molding sand tank.

[0007] Profitably obtained heat is used for heating domestic water and space heating.

[0008] Advantageously, in the absence of heat demand, the heated water from the first and second heat exchangers is sent to the emergency cooler and plate heat exchanger circuits.

[0009] Advantageously, the molding compound tanks sit on tubular heat exchangers.

[0010] The essence of the invention in terms of the system is that the system consists of at least two moulding sand cooling modules, where each module contains a moulding sand tank equipped with a tubular heat exchanger and a recirculation tank, connected by piping to the plate heat exchanger circuit and the emergency cooler and water buffer tank.

[0011] Advantageously, tubular heat exchangers consist of a bottom segment and an upper segment.

[0012] Advantageously, the tubular heat exchanger is set on a support structure.

[0013] Advantageously, the support structures, heat exchanger segments and tanks are connected to each other by flanged connections

[0014] The proposed two-stage heat recovery system and method of cooling the molding sand has several advantages. First, there is a favorable temperature distribution in the system, which is important for the condition of pipes and heat exchanger fins. Thanks to the use of water recirculation, water can be heated to high temperatures, up to 90° C, without additional equipment in the form of heat pumps or heaters. The system can operate in multiple scenarios, such as heat storage, molding sand cooling or single-stage operation, which increases its functionality. It can be easily expanded, making it possible to cool larger quantities of molding sand. By using the solutions of the invention, it is possible to heat production halls or office spaces, as well as to obtain hot water for ongoing use in the foundry.

[0015] The solutions according to the invention are illustrated by an example of implementation in the figure, where Fig. 1 shows a schematic of the two-stage heat recovery system, Fig. 2 - the way of loading the recirculation tanks, Fig. 3 - the way of loading the buffer tank, Fig. 4 - the way of cooling the molding sand without loading the recirculation tanks, Fig. 5 - a general view of the molding sand tank with heat exchanger.

[0016] The object of the invention is a system for the two-stage cooling of molding sand and the extraction of the heat lost by the molding sand in this process, which is then used for heating office and production premises and domestic water.

[0017] The system has two modules containing tanks 1.1 and 1.2 for molding compound set on tubular heat exchangers 2.1. and 2.2. connected to recirculation tanks 3.1. and 3.2. Heat exchangers 2.1. and 2.2 consist of two segments, a lower segment (14) and an upper segment (14'), with the lower segments (14) seated on support structures 4. The support structures 4, the segments of heat exchangers 2.1 and 2.2, and the tanks 1.1 and 1.2. are connected to each other by flanged connections. In addition to the modules, the system includes a plate heat exchanger circuit 5 and a fan-type emergency cooler 6, to which a 35% glycol-in-water solution 11 is fed, and a thermally insulated water buffer tank 7. As shown in Fig. 1-4, the system can be connected to water air heaters 8 in an industrial facility, to a central heating system 9 in an office building, and to a domestic water system equipped with a buffer tank 10 into which cold mains water 12 is fed and hot water 13 is discharged to existing DHW storage tanks.

[0018] The molding mass at a temperature of about 400 °C is placed in tank 1.1. equipped with tubular heat exchanger 2.1. and the water in it receives heat in the process of cooling the molding mass to about 200 °C. The heated water is sent to the recirculation tank 3.1. and the molding compound is placed in the second tank 1.2. where it is further cooled to a temperature of 60 to 40 °C by the water in the heat exchanger 2.2., sent to the recirculation tank 3.2. and from there to the recirculation tank 3.1. as shown in the diagram of Fig. 1 and Fig. 2, where it is mixed with water of higher temperature and then sent to the water buffer tank 7, as shown in Fig. 3. The water heated up to 90°C is stored in the thermally insulated buffer tank 7, and then used for heating domestic water and space heating.

[0019] In the absence of heat demand, recirculation tanks 3.1 and 3.2 are omitted, and hot water is directed to the circuit of plate heat exchanger 5 and cooler, from where it is removed as steam to the environment, as shown in Fig. 4.

Claims

1. A method of recovering waste heat generated in the process of cooling the molding sand, characterized by the fact that the molding sand is placed in tanks (1.1., 1.2.) equipped with tubular heat exchangers (2.1., 2.2.), and the heat coming from the molding sand is collected in two stages by means of water contained in tubular heat exchangers (2.1., 2.2.) connected to recirculation tanks (3.1., 3.2.) and is stored as water heated to a temperature of up to 90°C in a thermally insulated buffer tank (7), with the first stage lowering the temperature of the molding sand from about 400 to about 200°C and obtaining water at a temperature of not less than 60°C, and the second stage lowering the temperature of the molding sand from about 200 to 60-40°C and obtaining water at a temperature of not less than 40°C.

2. The method according to claim. 1, characterized by the fact that heated water contained in tubular heat exchangers (2.1., 2.2.) is transferred through pipes to recirculation tanks (3.1., 3.2.).

3. Method according to claim. 1, characterized by the fact that heated water from the first recirculation tank (3.1.) connected to the heat exchanger (2.1.) of the molding sand tank (1.1.) is sent through pipes to the main water buffer (7), and water of lower temperature from the heat exchanger (2.2.) of the moulding sand tank (1.2.) is sent through pipes to the recirculation tank (3.1.) and mixed there with the higher temperature water coming from the heat exchanger (2.1.) of the moulding sand tank (1.1.).

4. The method according to claim. 1, characterized by the fact that the heat obtained is used for heating domestic water and space heating.

5. Method according to claim. 1, characterized by the fact that in the absence of demand for heat, the heated water from the modules is sent to the circuit of the emergency cooler (6) and the plate heat exchanger (5).

6. method according to claim. 1, characterized by the fact that the molding compound tanks (1.1., 1.2.) are seated with tubular heat exchangers (2.1., 2.2.).

7. A system for waste heat recovery with at least one heat exchanger, characterized in that it consists of at least two moulding sand cooling modules, where each module contains a moulding sand tank (1.1., 1.2.) equipped with a tubular heat exchanger (2.1., 2.2.) and a recirculation tank (3.1., 3.2.), connected by piping to a circuit of a plate heat exchanger (5) and an emergency cooler (6) and a water buffer tank (7).

8. system according to claim. 6 characterized by the fact that the tubular heat exchangers (2.1., 2.2.) consist of a bottom segment and an upper segment.

9. system according to claim. 6, characterized by the fact that the tubular heat exchanger (2.1., 2.2.) is seated on a support structure (4).

10. system according to claim. 6 characterized by the fact that support structures 4, heat exchanger segments (2.1, 2.2) and tanks (1.1, 1.2.) are connected to each other by flanged connections (14).

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