Topic3. Boiler paths. Boiler layout. Classification and designation of steam and hot water boilers
Fuel, steam-water, air, gas paths and path
ash and slag removal; schematic diagram of the steam-water path of a drum boiler with
natural, multiple forced circulation and direct-flow;
Schematic diagram of the gas-air path of the boiler with balanced draft.
Boiler layout (P-, T-, U-shaped, three-way, tower). KA classification
(by purpose, by issued working body, by relative location
combustion products and working fluid, according to the method of creating the movement of the working fluid,
according to the pressure of the generated steam, according to the installation method). Designation of steam and
hot water boilers.
Boiler unit ducts
The main paths of the boiler are fuel, steam, air,
gas and ash removal path.
fuel tract - complex
elements in which the supply, processing (crushing, grinding,
heating, etc.), transportation and supply of fuel to the combustion chamber for
incineration.
The solid fuel path includes: crushing equipment, conveyors,
crushed fuel bunker, coal mill and dust pipelines.
The liquid fuel path includes: a drain device, tanks for
storage, coarse and fine mechanical cleaning filters, transfer pumps,
fuel oil heaters, measuring instruments (pressure, flow, temperature).
The gaseous fuel path consists of a gas control point,
which includes a gas pressure regulator, safety fittings, a filter
mechanical cleaning, measuring instruments (pressure, flow, temperature) and
etc., and gas pipelines.
steam-water tract is a system in series
included elements of equipment in which feed water moves,
steam-water mixture, saturated and superheated steam (on boilers with superheated steam)
(Fig. 3.1).
Rice. 3.1. Schematic diagram of the steam-water path of the boiler: a –
drum with natural circulation; b - drum with repeated
forced circulation; v —
direct-flow; 1 - feed pump; 2
– water economizer; 3 - drum; 4 - downpipes; 5 - collector; 6 -
lifting pipes of evaporative heating surface; 7 - superheater; eight -
circulation pump; I - feed water; II - superheated steam.
The steam-water path of a drum boiler generally includes: an economizer,
outlet pipes (connecting the economizer to the boiler drum), drum, downcomers
pipes and lower distribution manifolds, flue screen pipes (lifting
pipes), superheater.
According to the type of steam-water path, drum ones are distinguished (in which the movement
(circulation) of water occurs in a closed circuit (upper drum - lowering (unheated pipes) - lower drum (collector) - screen (heated pipes) - upper drum)) and once-through boilers.
Air tract - complex
elements of equipment for receiving atmospheric (cold) air, its
heating, transportation and supply to the combustion chamber. air path
includes: cold air box, draft fan, air heater
(air side), hot air box and burners.
The air path (except for the intake duct) usually operates under
overpressure developed by a blower fan.
Gas tract - complex
elements of equipment through which the movement of combustion products is carried out
before releasing into the atmosphere. The gas path starts in the combustion chamber, flue gases
sequentially pass through the superheater (if any),
economizer, air heater (gas side), ash collector
(installed when burning solid fuel) and then the smoke exhauster is fed
through the chimney to the atmosphere.
Process automation code
The boiler unit is a technically complex device. As a multidimensional object, it contains many control systems. Many technological parameters must be maintained for reliable and economical operation of the boiler. These main parameters are:
- Boiler heat load system:
- combustion process in the furnace;
- air supply to the boiler furnace;
- rarefaction in the furnace;
- Superheated steam temperature control system;
- Boiler supply control system.
Boiler supply control system | the code
Steam boiler power regulation is carried out in the following way. It is assumed that the maximum allowable deviation of the water level in the drum is ±100 mm from the average value. A decrease in the level can lead to disruptions in the supply and cooling of water pipes. Increasing the level can lead to a decrease in the efficiency of intradrum devices. Overfeeding the drum and throwing water particles into the turbine can cause severe mechanical damage to its rotor and blades.
Three-pulse automatic control system for supplying water to a drum steam generator
Regulation schemes. Based on the requirements for regulating the water level in the drum, the automatic regulator must ensure the constancy of the average level regardless of the load of the boiler and other disturbing influences. water and steam. This task is performed by a three-pulse controller.
The regulator moves the valve when an imbalance signal appears between the flow rates of feed water Dpv and steam Dpp. In addition, it acts on the position of the supply valve when the level deviates from the set value. Such ACS supply, combining the principles of regulation by deviation and disturbance, is most widely used on powerful drum boilers.
Regulation of the water regime of the boiler unit | the code
Regulation of the water regime of the drum steam boiler
The chemical composition of the water circulating in drum boilers has a significant impact on the duration of their non-stop and non-repair companies. The main indicators of the quality of boiler water are the total salt content and the excess concentration of phosphates. Maintaining the total salt content of boiler water within the normal range is carried out with the help of continuous and periodic blowing from the drum into special expanders. Boiler water losses with blowdown are carried out with feed water in the amount determined by the water level in the drum. Continuous blowdown is controlled by actuating the regulator on a control valve in the blowdown line. In addition to the correction signal for salinity, the input of PI-controller 2 receives a signal for the blowdown water flow rate Dpr and a signal for the steam flow rate Dpp. The steam flow signal is sent to the flow meter 3, the electromechanical integrator of which is used as a pulser, acting through the starting device 4 to turn on and off the plunger phosphate pump 6.
Boiler frame with ladders and service platforms
frame - a metal structure of columns, beams and ties that are installed on the foundation and are designed to connect and fasten the elements of the boiler.
A frame is a metal structure designed to install drums on it and fasten all heating surfaces, lining, platforms, stairs and other parts and structures of the boiler.
The frame of a medium-sized boiler consists of vertical columns installed on the foundation, supporting and auxiliary horizontal beams, trusses and connecting crossbars. The main elements of the frame, as a rule, are taken out of the brickwork, and heating of its elements is not allowed above 70 C.
For convenient and safe maintenance of the boiler, its fittings and fittings must be installed permanent stairs and platforms from fire-resistant materials, equipped with metal railings.
Metal platforms and steps of stairs can be made:
- a) from corrugated sheet steel or from sheets with a non-smooth surface obtained by welding or in another way;
- b) from honeycomb or strip steel (per edge) with a mesh size of not more than 12 cm2;
- c) from expanded metal sheets.
It is forbidden to use smooth platforms and steps, as well as to make them from bar (round) steel.
Ladders with a height of more than 1.5 m, intended for the systematic maintenance of equipment, must have an angle of inclination to the horizontal of not more than 50 degrees.
The dimensions of the stairs must be: in width - at least 600 mm, in height between steps - no more than 200 mm, and in width of steps - at least 80 mm. Stairs should have landings every 3-4 m in height.
The width of the platforms intended for maintenance of fittings, instrumentation and control devices must be at least 800 mm, and the rest of the platforms - at least 600 mm.
The vertical distance from the service platforms of water indicating devices to the middle of the water indicating walls must be at least 1 m and not more than 1.5 m.
The platforms and the upper part of the lining of the boilers from which maintenance is carried out must have metal railings with a height of at least 0.9 m with a continuous sheathing along the bottom to a height of at least 100 mm.
The supporting structures of the boiler are its most important elements, ensuring the safety of operation. Therefore, it is necessary to monitor their safety, carrying out timely repairs, to prevent heating of beams and especially columns, collapse of brickwork.
drum boilers
Water circulation in forced circulation drum boiler 1 Feed pump 2 Economizer 3 Lift pipes 4 Down pipes 5 Drum 6 Superheater 7 To turbine 8 Circulation pump
Water supplied to the boiler by a feed pump (for example, a steam injector), after passing through the economizer, enters the drum (located at the top of the boiler), from which, under the action of gravity (in boilers with natural circulation), it enters the unheated down pipes, and then into the heated lifting pipes. where vaporization occurs (rising and descending pipes form a circulation circuit). Due to the fact that the density of the steam-water mixture in the screen pipes is less than the density of water in the down pipes, the steam-water mixture rises through the screen pipes into the drum. It separates the steam-water mixture into steam and water. The water re-enters the downpipes, and the saturated steam goes to the superheater. In boilers with natural circulation, the frequency of water circulation along the circulation circuit is from 5 to 30 times.
Boilers with forced circulation are equipped with a pump that creates pressure in the circulation circuit. The multiplicity of circulation is 3-10 times. Boilers with forced circulation in the territory of the post-Soviet space have not received distribution.
Drum boilers operate at less than critical pressure.
Classification code
By appointment:
- Power steam boilers - designed to produce steam used in steam turbines.
- Industrial steam boilers - produce steam for technological needs, the so-called "industrial steam generators".
- Steam recovery boilers - use secondary energy resources to produce steam - the heat of hot gases generated in the technological cycle. Power waste heat boilers as part of CCGT use the heat of gas turbine exhaust gases.
According to the relative movement of heat exchange media (flue gases, water and steam), steam boilers can be divided into two groups:
- gas-tube (fire-tube, flue) boilers
- water tube boilers
Water tube boilers based on the principle of movement of water and steam-water mixture
subdivided into:
- drumming (with natural ruen and forced circulation: in one pass through the evaporation surfaces, only part of the water evaporates, the rest returns to the drum and passes through the surfaces repeatedly)
- once-through (the medium between the inlet and outlet of the boiler moves sequentially without returning)
In water-tube steam generators, water and a steam-water mixture move inside the pipes, and the flue gases wash the pipes from the outside. In Russia in the 20th century, Shukhov's water-tube boilers were predominantly used. In gas pipes, on the contrary, flue gases move inside the pipes, and the coolant washes the pipes from the outside.
Notation | the code
Type-D-P-T-FOH
- A type
- Pr - with forced circulation (water from the drum is supplied to the evaporation surfaces by special pumps);
- Prp - with forced circulation and intermediate overheating of steam;
- E - with natural circulation (under the influence of the difference in the densities of water and steam);
- Ep - with natural circulation and intermediate superheating of steam;
- P - direct-flow;
- Pp - direct-flow with intermediate steam overheating;
- K - with combined circulation (natural in some surfaces, forced in others);
- Kp - with combined circulation and intermediate steam reheating.
- D
- Boiler steam capacity, t/h.
- P
- Pressure at the outlet of the boiler, MPa (previously often indicated in kgf / cm²)
- T
- Boiler outlet temperature, °C (not specified for boilers generating saturated steam). If the temperature after reheating differs from the temperature of the primary steam, it is indicated through a fraction.
- F
- Type of fuel (if the furnace is not layered):
- K - coal and semi-anthracite (lean coal);
- A - anthracite, anthracite fines (sludge);
- B - brown coal, lignites;
- C - shales;
- M - fuel oil;
- G - natural gas;
- O - waste, garbage;
- D - other types of fuel.
- O
- Type of furnace (not indicated for gas-oil, except for "B"):
- T - chamber furnace with solid slag removal;
- Zh - chamber furnace with liquid slag removal;
- R - layered firebox (grate);
- B - vortex furnace;
- C - cyclone furnace;
- Ф - a furnace with a boiling (fluidized) bed (stationary and circulating);
- And - other types of fireboxes, including two-zone ones.
- H
- "H" if the boiler is pressurized.
The parameters of the boiler, if possible, are selected according to the standard range. After the designation according to GOST, the factory brand can be written in brackets, for example, E-75-3.9-440BT (BKZ-75-39FB).
38 Why is a staged evaporation scheme with an external cyclone better than with a baffle installed inside the drum.
stepped
evaporation is that in water
volume of the boiler drum, zones are created
with different salt content in the boiler
water. This is achieved by separating
water volume of the boiler drum with its
heating surfaces into individual
compartments. Continuous purge is made
from the compartment with the highest salinity,
and the selection of steam with the smallest. Upper
the drum is divided by a partition
hole (overflow pipe) for two
compartment - clean and saline. Nutritious
water enters a clean compartment, and salt
powered from a clean compartment through
overflow pipe. In a clean compartment
about 80% of steam is formed, in salt
twenty%. Therefore, from pure to saline
compartment receives 20% of the boiler water, which
for a clean compartment is a purge.
Therefore, purge clean compartment
occurs without heat loss,
ensuring low salinity
boiler water in it.
essential
the disadvantage is the possibility
backflow of water into a clean compartment
with "sluggish" circulation. For elimination
this shortcoming is applied stepwise
evaporation with remote cyclones, which
are salt compartments (DKVR-20). At
use of remote cyclones in
as separation volume difference
levels in compartments can be selected
sufficient under the conditions of prevention
reverse flow of water. Therefore, schemes
with remote cyclones are preferred,
especially at low performance
salt compartment.
Nutritious
water enters the drum, which serves
clean compartment. Purge water from
drum enters the cyclones, for which
this water is nutritious. Cyclone
has a separate circulation circuit and
delivers steam to the boiler drum. Steam passes
through the separation device
compartment and further cleaned.
Continuous purge is carried out
only from the cyclone, if there is one. At
stepwise evaporation decrease
heat loss with blowdown and increases
steam quality
Efficiency
stepwise evaporation increases with
increasing the number of evaporation stages,
however, this increase with increasing number
steps fades. Greatest
distribution received two- and
three step schemes. At the same time, the second
evaporation stage can be arranged
either inside the drum or outside it - in
portable cyclones. In a three-stage
scheme, usually the first and second stages
perform in the drum, and the third - in
portable cyclone.
stepped
evaporation improves purity
steam at a given nutrient quality
water and a given purge value. It
also makes it possible to obtain a satisfactory
steam purity with lower water
quality, which makes it easier and cheaper
water treatment. Staged evaporation
also improves the economy
steam turbine plant due to
reduction in blowdown without noticeable
reduction in steam quality.
Evaporating surfaces of the boiler
Earlier it was noted that the main elements of the boiler are: evaporative heating surfaces (wall tubes and boiler bundle); superheater with steam superheat regulator; water economizer, air heater and draft devices.
Steam-generating (evaporative) heating surfaces differ from each other in boilers of various systems, but, as a rule, they are located mainly in the combustion chamber and perceive heat by radiation - radiation. These are screen pipes, as well as a convective (boiler) bundle installed at the outlet of the furnace of small boilers (Fig. 7.15).
Rice. 7.15. The layout of the evaporative surfaces of the drum boiler unit:
- 1 — the contour of the lining of the firebox; 2, 3,4— side screen panels; 5 - front screen; 6 — screen and convective beam collectors; 7 - drum;
- 8 - festoon; 9 — convective beam; 10— back screen
The screens of boilers with natural circulation, operating under vacuum in the furnace, are made of smooth pipes (smooth-tube screens) with an inner diameter of 40-60 mm. The screens are a series of vertical lifting pipes connected in parallel with each other by collectors (see Fig. 7.15). The gap between the pipes is usually 4-6 mm. Some screen pipes are inserted directly into the drum and do not have upper manifolds. Each panel of screens, together with the downcomers placed outside the lining of the furnace, forms an independent circulation circuit.
The pipes of the rear screen at the point of exit of the combustion products from the furnace are bred in 2-3 rows. This discharge of pipes is called festooning. It allows you to increase the cross section for the passage of gases, reduce their speed and prevents clogging of the gaps between the pipes by molten ash particles that have hardened during cooling and carried out by gases from the furnace.
In high-power steam generators, in addition to wall-mounted ones, additional screens are installed that divide the furnace into separate compartments (Fig. 7.16). These screens are illuminated by torches from two sides and are called double-light. They perceive twice as much warmth as wall-mounted ones. Double-light screens, by increasing the total heat absorption in the furnace, make it possible to reduce its dimensions.
Rice. 7.16. Placement of screens in the cross section of the furnace:
- 1 - front screen; 2 — side screens; 3 — back screen;
- 4 — two-light screen; 5 - burners; 6 — furnace lining outline
