Boiler water-heating equipment is widely used in industry, where the high performance of generating sets is appreciated. Such units are mainly used for technological operations - for example, for generating steam by evaporating water. But the possibility of household operation is not excluded, if you need to organize a hot water supply to several large consumers. Among the most optimized steam generator designs can be noted water pipe. A boiler of this type is not inferior to many analogues in terms of output per unit time, but its device causes many restrictions on operation in tight conditions.
Unit device
The most common design with two drums (collectors) at the base. These are metal tanks that are interconnected by pipes of different diameters. Also a required component is a combustion chamber or firebox that generates thermal energy. The remaining structural elements include:
- A pipe for supplying fuel (usually liquid).
- Circulation communications for water.
- Entrances and exits for water.
- Outlet for draining water.
- Partitions (if it is a closed boiler system in a protective housing).
- Chimney.
- Steam separator.
Most of the structural elements of the water tube boiler are made of heat-resistant steel alloy. There are also cast-iron models, but they can be used if the operating conditions allow the installation of heavy units. Tubular and fittings can partially be performed on the basis of fire-resistant ceramics, which is more practical than metal. The furnace window and a number of other areas of possible observation are made of heat-resistant tempered glass.
Auxiliary structural elements
Optionally, the boiler may include additional devices that expand the capabilities and ease of use of the equipment. Among them, the following devices can be noted:
- Superheater. Designed to increase steam temperature to 100 ° C and above. The design of the water tube assemblies alone does not aim to bring the temperature regime of steam to certain values. As a rule, the target point of the work is the effect of evaporation. In turn, convection superheaters depending on the model are able to bring the temperature of the outlet mixture to 500 ° C, which may be required in some technological operations in production.
- Dehumidifier. It’s also a steam preparation that makes it dry, removing excess moisture.
- Steam battery. If the water tube boiler does not cope with the loads or, conversely, fills the steam chamber in minimal volumes, this device will help to balance the operating mode. The battery draws or injects steam into the system when necessary.
- Device for water treatment. Water, as a source of generation, also needs appropriate treatment. For example, a special filter system reduces the volume of dissolved oxygen, removes salts and unwanted chemicals.
- Today, it is less and less dispensed with automatic controls, but they are also supplied as standard with equipment. You can only purchase an extended set of instrumentation that will allow you to comprehensively monitor the parameters of pressure, temperature, humidity, etc.
Operating principle
In the initial position, two drums are filled with water - one completely (water), and the second (steam) half. In the second collector, a separation membrane is provided inside that separates water from steam. This boundary is called the evaporation mirror. The workflow starts from the moment the furnace fires up, which is coupled to the heat exchanger in the form of a tubular system with circulating water. Hot water enters the first drum, maintaining sufficient volume in it.
In parallel, the process of evaporation of the liquid in the steam manifold of the water tube boiler begins. The principle of operation of the unit is based on convective heat transfer, which can be performed in a natural non-stop mode. Cold water from the central water supply system passes the basic filtration level, then enters the heat exchange system and is sent to the heating drum. Further, depending on the rate of evaporation, the liquid gradually replenishes the filling level of the steam collector. Steam, in turn, is either discharged through the chimney, or enters the process zone for further use.
Differences from the fire tube boiler
The difference between these units is in the configuration of the location of the combustion chamber or, in principle, the source of thermal energy relative to the heat exchanger and the tank with water. Firstly, steam generation is not necessary at all. The fire tube boiler mainly works for water heating, providing the function of a domestic hot water system. Secondly, in such boilers, the furnace is located in the center of the structure, and tanks with water circulation circuits are of an applied nature. They are in contact with the heat exchanger on the outer surface of the structure.
But not only this differs fire tube and water tube boilers. The difference also passes through the means of regulating the heat exchange process. An economizer is provided in the design of the water tube unit, due to which initially cold water is pre-heated. Accordingly, further heat transfer reactions proceed more intensively and with less energy consumption. On the other hand, the advantages of the fire tube equipment include structural simplicity and the minimum amount of maintenance measures during operation.
Differences from gas pipe equipment
In water tube units, the direct translator of thermal energy is hot water, which fills the circulation pipes of the heat exchanger. It turns out an efficient and safe generator that contributes to the production of steam. As for gas-tube boilers, the technical design, even externally, can partially correspond to water-tube structures. The only difference is that the exhaust gases in the combustion chamber will be the carrier of thermal energy. How does this affect the operational process? If the principle of operation of a water tube boiler allows the total consumption of production products without residues until the moment of vaporization and further use of steam, then the gas tube boiler will already have to release a working gas medium in the heat exchanger system. Moreover, thick branch pipes are provided for this to ensure process safety.
Varieties of a water tube boiler
The main classification feature is the location of the collectors. Traditionally, constructions are equipped with horizontal drums, which are conveniently connected to circulating water supply circuits. Two collectors are installed on the platform in parallel, and between them a firebox with branch channels can be placed. If there is not enough space in the technical room, then vertical water tube boilers on a special communication substrate are used. Cylindrical drums rush up, and a working fluid with different temperature indicators is supplied from below. Process steam is discharged at the top.
Ship water tube boiler
The design of such units is optimally suited for use in marine transport. But in this case, special modifications of boilers are used - radiation ones. Their distinguishing feature is the use of radiation thermal energy, which is also released during the combustion of fuel (usually diesel). An obligatory structural condition is the upper arrangement of the nozzles of the furnace. Another feature of the device for a water tube boiler for marine vessels is the combination with steam turbine units that provide intermediate steam heating.
Equipment maintenance
Communication infrastructure with piping elements is rather complicated for water pipe units, which leads to an extensive list of technical measures for diagnosis and repair. Maintenance personnel must periodically check the condition of the pipes for leaks, perform a flaw detection of functional units and automatic controls, as well as maintain reliable connections with fasteners. Particular attention is paid to the piping of the heat exchanger and collectors - the slightest pressure drop can damage the structure, which will create conditions for the depressurization of the circuit.
Design advantages
The most important advantage of such boilers in the general family of steam units is safety. Maintaining an optimal temperature balance, you can count on long-term operation of the equipment without accidents and damage to the working bodies. The wide regulatory capabilities of the water-tube cat are also noted, which is confirmed by the integration of the economizer with automatic shut-off valves. Devices operate without operator intervention, based on data from established thermostat algorithms. This makes it possible to program the system for several days in advance.
Design cons
The principle of operation of such boilers is focused on high performance regardless of application conditions. Recently, this nuance has played an increasing role against the background of optimization and rationalization of production capacities. The massive body and multi-level communication interchanges of steam water tube boilers make us look for alternative solutions to steam generation problems. However, the concept of minimizing the device of this boiler is not excluded. But in this case, high efficiency will be lost, not to mention the possibilities of working in the cogeneration mode with the parallel provision of the hot water supply. In other words, the equipment is optimally suited for large industries that require large volumes of process steam, but is hardly useful for supplying consumers with low demand for target energy.
Conclusion
The fundamental difference between the concept of water tube boilers is their belonging to the class of direct-flow equipment. Such plants have a significant advantage over autonomous systems, which consists in the possibility of a continuous generation process. Even at peak operating conditions, water tube boilers are able to function for a long time while maintaining the same quality of steam production. Another thing is that safety requirements nevertheless exclude long sessions of operation at high capacities. With regard to autonomy, then with respect to such boilers it is expressed in the elimination of the need for energy supply. Of course, the shut-off valves will need to be powered by at least a battery, but the process of water circulation and subsequent evaporation is completely dispensed with electricity.