Technical field

The invention relates, generally to the design of the heat recovery unit of a smelting aggregate as a draft system of heat exchangers, which re-acquire low and medium potential waste heat from smelting aggregates particularly those with high drift of dust particles contained in the exhaust gas. The invention pertains generally to the field of engineering, mostly to the steel industry.

The prior art

Use of industrial waste heat is one of the most important tools for reduction of energy consumption and elimination of CO ₂ emissions in the industry. There are a number of system solutions that use waste heat from smelting aggregates. Devices that are used to exchange energy between systems and objects with different parameters are known as heat exchangers. In the steel industry a variety of recuperative heat exchangers is used for the waste heat recovery.

The bulk of currently commercially available heat exchangers are designed for use in heavy steel industry, given the aggressive environment of flue gases and their high adhesiveness.

Aforementioned drawbacks evoked a proposal of a system for recovering heat from flue gases from the smelting aggregates, which would be able to work even in such environment, taking into account the specific requirements. These specific requirements can be classified mainly as provision of a simple and effective cleanability of heat exchanging surfaces from the flue gas sediments, and adaptation of the design to simple interchangeability of the main parts in contact with the flue gases.

The result of this effort is the newly created unit designed for recovery of heat from the flue gas waste heat of the smelting aggregate. It is a recuperation unit implemented as a system of heat exchangers.

Summary of the invention

Vyssie uvedene nedostatky zo stavu techniky odstranuje rekuperacne zariadenie taviaceho agregatu ako system vymennikov tepla pre taviaci agregat podl'a tohto vynalezu. The system that uses flue gas heat from a technological process of smelting in a smelting aggregate receives waste heat contained in the flue gases and transfers it to the supply air for combustion of natural gas in its own recuperative burner, as well as to the plant energy system for water heating. Simultaneously it provides cooling of flue gas. A thermal unit is a smelting furnace heated by a gas burner. The furnace is a chamber type. Combustion products are discharged via chimney to the fume hood, where cool air is admixed in order to reduce the temperature for the operating filters. The essence of the technical solution according to the utility model lies in the fact, that it consists of two basic consecutive functional parts, namely a Heat exchange equipment combustion products - air with a preheated air outlet to the burner; and Heat exchange equipment combustion products - water with a hot water outlet. Linking of the Heat exchange equipment combustion products - air and Heat exchange equipment combustion products - water is ensured by a flue gas duct. This system also includes elements for the obstruction and control of flow, rotary flaps or sliding valves and flexible hose jumpers for air conduction.

Heat exchange equipment combustion products - air also provides flue gas exhaust from the smelting aggregate and subsequently it transports the flue gases to the second Heat exchange equipment combustion products - water. The heating in the Heat exchange equipment combustion products - air is ensured by a flue gas piping system, which is equipped with a steel casing. This casing creates a space around the flue gas pipeline, through which cool air is forced against the flue gas flow supplied from the connected tangential fan or blower. The fan or blower placed on the floor can force air directly into the burner and/or the forced air is ducted through the cooling spaces around the flue pipes by a solid steel cover casing and flexible hose jumpers to the already preheated burner. This concept is designed so that the preheated air outlet is situated at the flue gas inlet of the Heat exchange equipment combustion products - air, and cool air inlet is situated at the flue gas outlet of the Heat exchange equipment combustion products - air; while the Heat exchange equipment combustion products - air consists of at least three segments arranged in three spatial axes, where a art of segments is revolvable and a part of segments is firmly anchored. S vyhodou su dva segmenty stoSitel'ne ajeden segment je pevne kotveny. This means that a flue gas pipe concentrically stored in a solid steel casing is conducted centrally through each segment of the Heat exchange equipment combustion products - air. Thereby the cooling spaces around flue gas pipes are created with tangential air inlets/outlets located at their ends. Elbows are installed at the bending points of the flue gas pipes, i.e. the segments themselves. They serve as inspection or cleaning openings. A shorting branch leads from the flue gas pipeline to the chimney at the end of the Heat exchange equipment combustion products - air.

Heat exchange equipment combustion products - water used to heat domestic hot water is closed by a water circuit. It is formed by a vertical flue gas chamber with horizontally arranged field tubes in which heated water flows. Flue gas flow direction is upwards from the bottom with flue gas outlet into the chimney. Due to assembly and disassembly, field tubes are divided into segments, allowing their easy replacement in case of a failure. Flue gas chamber is accessible from three sides via openable doors allowing easy and efficient cleaning. Flue gas and water flow is controlled by flaps, gate valves and valves controlled by an automatic control system. If necessary, they can be controlled manually.

The basic functional part of the exchanger is a field tube. It is a tube in a tube: the water flows from one segment space through an inner tube to the end of the tube, where the current is reversed and water flows back via a cross-section of the annulus to the second segment space. Field tubes with functional spaces for the flue gas flow fill the entire cross-section of the flue line. Flue gas flows perpendicularly, i.e. transversely to the tubes. The tubes are arranged in groups. The segments are interconnected by hoses so that the water flowing from the inlet to the heat exchanger flows parallelly in two branches to the outlet from the heat exchanger. In the lower area of the flue gas inlet, there is a cleaning opening similar in construction to vertical walls.

Benefits of the recuperative unit for recovery of waste heat from the flue gas from the smelting unit according to the invention result from the effects which are reflected in operation. The effects consist mainly in the fact that the designed construction allows for easy and efficient cleaning of the heat transfer surfaces from flue gas deposits, which impair heat transfer. The design also allows for easy interchangeability of corroded parts that come into contact with the flue gases, As the research of materials demonstrated significantly higher corrosion resistance of steel or cast iron, we chose to use affordable materials and possibility of their replacement in case of corrosion. Specific conditions of smelting aggregates such as furnace tilting and existing dispositional options of the furnace itself, the surrounding technological equipment and areas in the production hall led to the installation of all parts of recuperative unit for flue gas waste heat recovery from the smelting aggregate on the furnace and in the immediate vicinity of the furnace.

Description of drawings

Recuperative unit for flue gas waste heat recovery from the smelting aggregate recasting secondary aluminium will be explained in more detail in the accompanying drawings, in which Fig. 1 demonstrates a side view of the system solution with two series-connected heat exchangers: the Heat exchange equipment combustion products - air followed by the following Heat exchange equipment combustion products - water. Fig. 2 shows a system solution of the Heat exchange equipment combustion products - air. Fig. 3 illustrates a top view of a system solution with two series-connected heat exchangers: Heat exchange equipment combustion products - air and behind it Heat exchange equipment combustion products - water. Fig. 4 shows a system solution of the Heat exchange equipment combustion products - water. It is understood that the various implementations of the invention shown in the various figures are represented for illustration and not as limitation to specific implementation. It is also understood that the various implementations of the invention shown in the various figures are made of materials known to professionals skilled in the art.

Using no more than routine experimentation, the professionals skilled in the art shall find or shall be able to ascertain equivalent implementations of the invention. Such equivalents shall also fall within the scope of the following claims.

Example of implementation

This example of a specific implementation describes a recuperative unit of the smelting aggregate constructed in accordance with the invention schematically shown in Fig. 1 and 3. It is a system of heat exchangers, which is located on the furnace and next to the furnace of the smelting aggregate. Flue gases from the furnace of the smelting aggregate transmit heat first to the air for its own recuperative burner, and then to the water into the boiler for heating and heating of domestic hot water, and then they escape to the chimney.

The entire recuperative unit is divided into two main functional units, namely heat exchange equipment (1) combustion products- air and heat exchange equipment (3) combustion products - water with other complementary and fixing elements. Heat exchange equipment (1) combustion products- air consists of a system of modules installed into a functional unit. There are three segments 8 of flue pipes, four elbows 10 with inspection openings, a swivel joint, flue gas pipe with a T-shaped short-circuit branch J_l_ and other elements 12 such as closing valve at the flue gas inlet, two closing flaps, ancillary equipment such as brackets and stands and other connecting components as shown in Fig. 2. Elbows 10 made of steel sheet are installed in the spots of change of flue direction by 90°. They are protected internally from the heat of the flue gas by an insulating layer of refractory concrete. One entire wall serves as an inspection opening as well as a cleaning opening. The closure of the opening has a shape of the door on hinges. It is sealed by a cord and secured with wedge lock and wing nuts.

Flue duct system consists of thick steel tubes, which also function as a heat transfer surface for air heating into the recuperative burner. For reasons of thermal dilation, they include telescopic expansion elements sealed by cords and liners. They are mounted to fittings and elbows 10 with flanges and screws. The area for heated air around the flue duct system is formed by thin-walled steel tubes of the casing, fitted on the pipes of the flue duct system in a demountable manner. Three areas for heated air are interconnected by flexible hose jumpers 13 for air conducting in series, forming a path for one air flow from the fan to the steel pipes leading to the burner. Air enters the heat exchange equipment (1) combustion products- air tangentially; progresses spirally around the inner pipe of the flue duct and escapes tangentially again. In the axis of furnace rotation i.e. furnace tilting, at the discharge of the melt, the flue pipe is formed into a swivel joint. It has a simple design with axial swivelling of the movable part. Connecting sealing has a gap for the air intake induced by a suction effect from the flowing flue gas. For the proper function of the joint, it must be placed exactly in the axis of pins of furnace tilting.

The last section of the flue duct placed between the heat exchange equipment (1) combustion products- air and heat exchange equipment (3) combustion products - water also serves as an exchanger with the same design as the heat exchange equipment (1) combustion products- air. It will, however, have its own cooling/heating circuit designed for other technological purposes determined by operation. The closing slide valve at the inlet of flue gas from the chimney into the flue duct has a steel construction. It is equipped with a layer of refractory concrete at the contact points with flue gases. It is fitted to the chimney and flue duct by flanges. Slide valve movement is provided by a motion screw. The closing flaps are situated at the output from the flue duct where the exchangers for heating of air to the burner end. They are controlled by servomotor and joined together e.g. electrically. One flap opens/closes the flue duct pipe section to the heat exchange equipment (3) combustion products - water; the second flap opens/closes the path to the chimney. These valves are used to control the amount of flue gas and hence heat to the heat exchange equipment (3) combustion products - water. In case of excess heat in the energy system of the operation, all flue gases are hereby transferred into the chimney. On the furnace and the floor, both exchangers and flue ducts are supported by brackets and stands whose height is adjustable during installation.

Flue gas flows from the furnace of the smelting aggregate through the open slide valve gradually through flue ducts and elbows. According to the position of flaps, the flue gases in the shorting T-shaped branch IT will continue by turning via a short-cut into the chimney, or further through the flue pipe into the heat exchange equipment (3) combustion products - water. Immediately behind the blower at the inlet from the fan, the air is divided and driven by two branches. It is a hot branch, which passes via flexible hose jumpers J_3 through individual segments 8 of the heat exchange equipment (1) combustion products - air against the flue gas flow, eliminating installation inaccuracies, and especially furnace tilting. Outlet from the heat exchange equipment (1) combustion products- air is a fixed tube mounted on the furnace, leading to the burner. Before entering the burner, the cold branch is connected.

Heat exchange equipment (3) combustion products - water shown in Fig. 4 consists of four main parts: the flue chamber and the system placed therein with field pipes for the flow of heated water. The design of the heat exchange equipment (3) combustion products - water comprises also two flaps at the inlet and outlet of the flue duct and other mechanical design elements, fittings, pipes and fasteners. The flue gas enters the heat exchange equipment (3) combustion products - water via a manually closable flap; it continues via diffuser sheet; passes through heat exchange tubes; continues via sheet concentrator of flow through manually closable flap into the chimney. Direction of flue gas flow is upwards from the bottom.

The basic functional part of the exchanger is a field tube. It is a tube in a tube: the water flows from one segment space through an inner tube to the end of the tube, where the current is reversed and water flows back via a cross-section of the annulus to the second segment space. Field tubes with functional spaces for the flue gas flow fill the entire cross-section of the flue line. Flue gas flows perpendicularly, i.e. transversely to the field tubes. The tubes are arranged in groups, segments. The segments are interconnected by hoses so that the water flowing from the inlet to the heat exchanger flows parallelly in two branches to the outlet from the heat exchanger.

Industrial use

Recuperative unit for flue gas waste heat recovery from the smelting aggregate, recasting secondary aluminium, according to this invention is a device usable in the steel industry with a sufficient amount of low and intermediate potential waste heat from the smelting aggregates particularly those with high drift of dust particles contained in the exhaust gas.