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Ministry of Education and ScienceRussian Federation

Education Agency

State Educational Institution of Higher Professional Education AltSTU named after. Polzunova I.I.

Department of Heat and Gas Supply and Ventilation »

Laboratory work

on the course “Heat generating installations”

“Thermal calculation of fluidized bed boilers”

Completed:

students TGV-31

O.D. Queen

YES. Lipezin

Checked by: S.M. Kislyak

Barnaul 2006

1. Fluidized bed zone

2. Output of calculated dependencies

2.1 Fluidized bed calculation

2.2 Calculation of heat transfer in the furnace

References

1. Fluidized bed zone

The basis for calculating a fluidized bed is the heat balance equation in the layer, which includes:

heat arrival:

Heat released when fuel burns in a fluidized bed;

Physical heat introduced into the bed by fluidizing air and fuel;

heat consumption:

With combustion products, excess air and ash removed from the layer;

Heat perceived by heating surfaces in contact with the NTKS material;

Heat for warming up the entrainment returned to the NTKS;

Heat removed from the layer by draining the ash (layer material).

The main problem is determining the proportion of fuel reacting in the layer (out of all burned fuel) and heat transfer to the heating surfaces. The proportion of coarse coke that burns out in the layer is determined by its grain characteristics, the fluidization rate and the intensity of particle recirculation. Those. In calculations, you need to use the grain characteristics of coke.

For practical calculations related to the design of new and reconstruction of existing boilers, in view of the sharply variable physical, thermophysical properties, particle size distribution of the fuel and the complexity of the processes, it is advisable to develop an approximate calculation methodology.

Taking into account the availability of proven methods for calculating the burnout of a pulverized coal flare, in the methodology for calculating LTFC (low-temperature fluidized bed) it is proposed to determine the consumption of burned fuel in the layer as the difference between the fuel burned in the layer and the fresh fuel burned in the above-layer volume and secondary (removal from the layer from the return for afterburning) by entrainment.

When calculating, it is necessary to take into account the change in the fraction of entrained particles D un, which depends on the operating speed in the layer w ks. The latter can only be determined after calculating the excess air. This circumstance leads to the need to introduce the dependence D un =f(w ks), which is linearized with sufficient accuracy in the operating speed range (37 m/s).

Thus, the proposed method makes it possible to calculate the main operating characteristics of a fluidized bed (excess air, velocity at the outlet of the layer, consumption of burnt fuel, air consumption under the grate) for given design characteristics and bed temperature.

Rice. 1. Diagram of a fluidized bed boiler

1 - air distribution system (air must be supplied to the bed for fluidization and combustion);

2 - system for removing ash and spent sorbent; 3 - supply system for coal and limestone; 4 - starting system (burner): 5 - coal and limestone; 6 - pairs; 7 - fly ash collection system: mechanical dust collector; bag filter; 8 - exhaust gases; 9 - thermal control system; 10 - ash; 11 - economizer; 12 - feed pump; 13 - line for returning ash with underburning to the fluidized bed

2. Output of calculated dependencies

2.1 Fluidized bed calculation

fuel heat exchange boiling temperature

The heat balance in the layer has the form:

(1.1)

where is the available heat of the fuel, kJ/kg;

sl - excess air in the layer;

--consumption of fuel burning in the layer, kg/s;

B -- fuel consumption introduced into the boiler, kg/s;

sl - layer temperature, K;

-- enthalpy of combustion products, air, ash at bed temperature, kJ/kg;

k j -- heat transfer coefficient to heat exchange surfaces, W/m 2 K;

H j - heating surface in contact with the fluidized bed, m 2 ;

t cf -- temperature of the working environment, K;

K ci - circulation rate (the ratio of the flow rate of the circulating material to the flow rate of the supplied fuel in the 1st and 2nd circuits);

t ci -- temperature of entrainment caught in the i-th ash collector, K;

t drain -- temperature of the drained ash (layer material), K.

The total multiplicity and circulation ratio in the 1st and 2nd circuits is determined from material balance for contours, and can be written as:

where: D=(1- 1)(1- 2)

1, 2 - integral efficiency of ash collectors 1, 2 stages.

Taking into account that J in В р =V in 0 s in t in В р =Q in s in t in, kJ/kg, and denoting:

equation (1.1) can be rewritten in a more convenient form:

The calculated consumption of fuel burning in the layer consists of the consumption of fresh fuel reacting in the NTKS volume larger than that carried over, as well as the carryover returned for afterburning, i.e.

Assuming that all entrainment returned for afterburning reacts in the volume of the layer, we have:

The fraction of entrained particles in the supplied fuel in the speed range of 37 m/s depends almost linearly on the operating speed of the gases at the exit from the layer w p, i.e.

D un =X+Yw r.

The operating speed of gases at the outlet of the layer is determined from the flow equation:

Having designated

The air flow rate supplied under the layer (to ensure a given excess air and temperature of the fluidized bed) is determined from (1.1a):

The excess air at the exit from the layer is (by definition) equal to:

2.2 Calculation of heat transfer in the furnace

To calculate the temperature of gases at the outlet of the furnace, the formula of the standard method is used:

T a - theoretical combustion temperature, K;

M is a coefficient that takes into account the nature of the temperature distribution along the height of the firebox;

y 0 = 5.67·10 -11 - black body emissivity, kW/(m 2 ·K 4);

w sr - average coefficient thermal efficiency of furnace screens;

F st - full surface combustion chamber walls;

b t - degree of blackness of the firebox;

c - heat conservation coefficient;

Vc cf - average total heat capacity of combustion products.

The use of this formula to calculate the above-layer volume of fluidized bed furnaces brings the calculation scheme closer to the traditional one, but requires clarification of the methodology and determination (taking into account the specifics of NTKS furnaces) of the adiabatic combustion temperature. The adiabatic temperature in this case is significantly lower than for the furnaces of layered and direct-flow flare boilers. This is due to the combustion of the bulk (up to 6090%) of the fuel directly in the volume of the layer, which has a fairly low temperature (1120-1220 K).

Thus, the expression for determining the heat release in the furnace (corresponding to the adiabatic combustion temperature) can be written as:

where: -- the maximum possible heat release in the furnace (i.e., the heat release that would occur when burning all the fuel in the above-layer zone)

Enthalpy of gases leaving the layer, kJ/kg,

Estimated fuel consumption, burning in the boiler and directly in the bed, kg/s,

K t - the proportion of fuel burned in the layer,

Heat introduced with secondary (cold or heated) air;

KJ/kg;(1.11)

Air flow to the boiler and introduced under the layer, nm 3 /s;

Heat introduced into the furnace with sucked air, kJ/kg;

Enthalpies of secondary and cold air, kJ/kg;

Heat introduced with recirculating gases and with gases ejected with entrainment from under the removed traps, kJ/kg;

The heat returned to the furnace with entrainment introduced into the above-layer volume is

KJ/kg (1.12)

where is the circulation rate of entrainment, the return of which is carried out above the layer,

с зл - heat capacity of ash (flyover) at temperature in the entrainment return system t c, kJ/kgK.

The adiabatic temperature is determined from the J-table with a calculated excess of air at the outlet of the furnace, taking into account the enthalpy of the ash equal to

where K c is the total circulation rate, determined by formula (1.2).

Under the same conditions, the enthalpy of gases at the exit from the furnace is determined, which is included in the expression for determining the average total heat capacity of combustion products Vc avg.

The ash concentration in combustion products is calculated as:

Boiler heat balance

Name of quantity	Dimension	Designation	Calculation formula
available fuel heat
consumption of fuel burning in the layer
heat loss from mechanical underburning			according to Appendix D-J
velocity of gases at the exit from the layer
air flow supplied under the layer
enthalpy of combustion products			according to Appendix B
enthalpy of air			according to Appendix B
enthalpy of ash			according to Appendix B
circulation rate
excess air leaving the layer

Thermal calculation of the combustion chamber

Name of quantity	Dimension	Designation	Calculation formula

outlet gas temperature
heat release in the firebox (max)
enthalpy of gases leaving the layer			according to the diagram
fraction of fuel burned in the layer
heat introduced with secondary air
heat introduced into the furnace with suction air
heat returned to the furnace
enthalpy of ash
ash concentration in combustion products

References

1. Thermal calculation of boiler units of low and medium power: Guidelines/ CM. Kislyak; Alt. state tech. University named after I.I. Polzunov. - Barnaul: AltGTU Publishing House, 2006.-57p.

2. Radovanovic. M., Combustion of fuel in a fluidized bed, - M.: Energoatomizdat, 1990. - 248.

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Combustion of fuels in a fluidized bed

Modern development energy and the worsening environmental situation in the world required the search and development of more progressive and environmentally friendly technologies for burning solid fuels.

One of promising directions, ensuring the environmental cleanliness of the use of solid low-grade fuels in power plants of the future, it should be considered their combustion in boilers with fluidized bed furnaces of various modifications: classical, circulating, aerospouting using aerospouting devices, since this significantly reduces emissions of SO 2 and NO x already by combustion stage.

1.1. Combustion of solid fuels in boiler furnaces with a classic fluidized bed

Rice. 1.1. Schemes of installations with a fluidized bed: a – classic fluidized bed: b – circulating fluidized bed; c – fluidized bed under pressure; 1 – main air; 2 – fuel supply; 3 – secondary air; 4 – ash output; 5 – return of entrainment; 6 – combustion products; 7 – cyclone; 8 – heating surface; 9 – turbine and compressor

In Fig. 1.1. A diagram of a furnace with a classic bubble fluidized bed is shown. In a bubbly fluidized bed at atmospheric pressure coal (or other solid fuel) is burned in a bed of solid particles (usually limestone), which is fluidized by combustion air supplied underneath the bed. The layer is heated with hot air or gases using a special gas burner. Fluidized bed boilers are designed so that the bed temperature is in the range of 815–870 o C. Possibility of operation at low temperatures leads to several benefits. Due to the low temperature, inexpensive materials such as limestone and dolomite can be used as a sorbent to bind SO 2. When limestone or dolomite is added to a layer, the reaction between CaO and SO 2 produces CaSO 4 . Depending on the sulfur content of the fuel and the amount of sorbent, SO 2 emissions can be reduced by 90% or more. Thermal nitrogen oxides are formed at temperatures above 1300 o C. As the temperature decreases, the reaction rate of NO x formation decreases greatly. At temperatures of 815–870 o C, the amount of NO x formed in the fluidized bed is significantly less than in traditional boiler plants operating at higher temperatures.

Fluidized bed combustion (FBC) technology has a number of advantages compared to pulverized coal combustion of solid fuels.

These include:

– simplicity of design;

– possibility of burning low-quality coals;

– safety in operation;

– absence of fine grinding mills;

– binding of SO 2 and SO 3;

– suppression of NO x (up to 200 mg/m3).

Due to intense mixing, the temperature is equalized throughout the fluidized bed, so the layer can be considered isothermal. Heating surfaces lowered into a fluidized bed have a very high heat transfer coefficient. This is facilitated by the destruction of the boundary layer on the heat transfer surface, as well as direct contact of particles with the heat removal surface.

The disadvantages of this combustion technology include abrasive wear of heating surfaces located in the layer; high values mechanical underburning, limiting the power of boiler units equipped with fluidized bed furnaces to 250 t/h. More powerful boilers require larger grates, which creates difficulties in ensuring uniform blast speed.

The ideal fuel for fluidized bed boilers is oil shale, which has high reactivity and high ash content, which determines the large mass of the material, and therefore the combustion temperature is stabilized, rapid drying of the fuel and good burnout occur.

When using low-ash Kansk-Achinsk coals, a large addition of inert material is required. The combustion of coals with a high content of alkali metal salts is very beneficial when used in fluidized bed furnaces, when practically no evaporation of salts occurs. This gives rise to the possibility of involving so-called “salty” coals in the energy sector.

An example of this is the industrial experience of introducing a fluidized bed for burning slag “salty” coals in the USA.

In 1986, Babcock-Wilcox converted the mechanically fired boiler at the Montana-Dakota Thermal Power Plant to a bubbly fluidized bed unit. This boiler was originally designed to produce 81.9 kg/s (295 t/h) of steam at a pressure of 9 MPa and a temperature of 510 o C for burning brown coal from the Belakh deposit.

However, the high content of sodium compounds in the fly ash led to severe slagging of the furnace and contamination of the superheater. Before reconstruction with a fluidized bed device, the power was limited to 50 MW with a design capacity of 72 MW. In order to avoid slagging and contamination of heating surfaces and ensure operation at full power, a fluidized bed was used. A new fluidized bed unit with a cross-section of 12.2 x 7.9 m was built into an old boiler with minimal changes screen surfaces working under pressure. The air distribution grille and its surrounding walls were cooled with water. A superheater and an evaporator were placed in the layer to provide the necessary steam production and steam superheating and limit the layer temperature at 815 o C. The gas velocity in the layer was 3.7 m/s, and the depth of the layer in operating condition was 1.37 m. To turn on and When the installation was launched, the air supply was carried out through eight sections. Since brown coal from the Belakh deposit is a highly reactive fuel, there was no provision for the return of fly ash. Taking into account low content sulfur and high content alkaline components in the fuel, sand was used as a layer material. The boiler was put into operation in May 1987. Now this unit carries a load of 80 MW without slagging or surface contamination. NOx concentrations measured were 0.14 g/MJ.

Ph.D. A.M. Sidorov, director,
Ph.D. A. A. Scriabin, Deputy Director for Science,
A.I.Medvedev, technical director,
F.V. Shcherbakov, chief engineer,
Research Center PA "Biyskenergomash", Barnaul, Altai Territory

On the feasibility of using furnaces with a forced low-temperature fluidized bed

A promising direction in the development of industrial and municipal energy is the introduction of highly efficient schemes for organizing the combustion process in a forced low-temperature fluidized bed (FFL). This technology ensures stable combustion in the volume of the layer and in the space above the layer. It allows the combustion of almost any type of fuel and combustible waste at a relatively low temperature (800-1000 °C) without sintering the layer.

Fireboxes with a classic bubble fluidized bed are characterized by low liquefaction rates and, accordingly, not very high thermal stresses of the air distribution grille (up to 3 MW/m2). The processes are carried out in the volume of the layer. Combustion above the layer quickly stops due to the rapid cooling of the flue gases, so all the blast must be supplied under the layer. The area above the layer and combustion screens are used with low efficiency; excess heat from the layer must be removed by heating surfaces immersed in it. As a result, fireboxes with a classic layer have a large area and are bulky. In addition, the operation of submerged surfaces is accompanied by intense abrasive wear. Despite low level layer temperatures, even a short-term cessation of liquefaction or a local increase in temperature is dangerous due to sintering of layer particles. This predetermines a narrow control range.

The main difference between FKS and other types of fluidized bed is the high (3-10 m/s) liquefaction speed - bed forcing. In this case, low mechanical underburning (less than 1.5-2.5%) is ensured due to the expansion of the cross-section of the combustion space above the layer towards the top. This promotes the return of large particles to the layer (recirculation) and reduces the removal of small particles. FKS does not have heating surfaces immersed in the layer and associated problems. Reliable operation of screen pipes in the area

the dynamic effect of the layer is ensured by the use effective means protection against abrasive wear.

Forced air distribution grille provides the following advantages:

■ ensures small dimensions of the grid and fluidized bed reactor and, therefore, favorable conditions for modernization and reconstruction of installed equipment, low cost and low repair costs;
■ allows you to burn fuel of coarser crushing compared to the classic fluidized bed; actually for brown coals maximum size a piece can reach 30-50 mm;
■ ensures more reliable operation of the layer according to the conditions of occurrence, and, consequently, expands the range of load control.

FKS technology implies operation of the layer in fuel gasification mode at actual values of excess air α<1,0. Величина избытка определяется калорийностью и видом топлива и может составлять 0,3-0,7 (для бурых углей больше). Это позволяет еще более уменьшить габариты реактора и снизить затраты на подачу воздуха под решетку. Высвободившийся воздух увеличивает долю вторичного дутья, необходимого для дожигания уноса и продуктов газификации, - до 70%, что позволяет организовать активное вихревое движение топочных газов, способствующее повышению эффективности сгорания топлива. Теплонапряжение воздухораспределительной решетки в расчете на поданное топливо может достигать 10-15 МВт/м2.

The FKS technology for forcing the air distribution grille is close to the circulating fluidized bed (CFB) and has the following advantages:

■ the ability to integrate FKS boilers into standard boiler cells;

■ absence of slagging of heating surfaces;

■ good performance of FKS fireboxes, compared to mechanized layer fireboxes, in terms of cost, service life, reliability and maintainability;

■ lack of mill equipment;

■ the ability to burn a wide range of fuels and combustible waste;

■ wide possibilities for regulating the operating parameters of FKS boilers and high stability of load carrying, which allows them to be used in conjunction with steam turbines;

■ high environmental performance in terms of emissions of sulfur and nitrogen oxides.

At the same time, compared to CFB, the introduction of forced fluidized bed technology requires significantly lower capital costs.

Particularly attractive options for implementing FCS are those associated with the reconstruction of boiler houses. They allow you to save and use most of the installed equipment, significantly reduce capital costs and, therefore, are affordable for most industrial energy and utility companies. At the same time, the invested funds quickly pay off and profitability increases.

Typically, the basis for introducing FCC technology is:

■ new construction with the ability to work on low-grade coal;

■ the need to ensure reliable heat and energy supplies (for example, by replacing fuel, expanding the range of coal used, using local low-grade fuels or combustible waste);

■ the need to reduce fuel costs by replacing it with cheaper ones, or by increasing the efficiency of its combustion;

■ the need to replace outdated, worn-out equipment;

■ the need to dispose of combustible waste, such as waste from coal preparation, timber and wood processing, slag from layer boilers, etc.

Experience in operating boilers with FCS

To date, we, together with a number of enterprises, have implemented furnaces with FCS at more than 50 facilities. As examples, we will give, in our opinion, the most interesting of them.

Example 1. Reconstruction of the Chita CHPP-2 with the conversion of layer boilers to combustion of Kharanorsky coal in a fluidized bed. In the period 1999-2003. Using FKS technology, a complete reconstruction of the Chita CHPP-2 was carried out with the transfer of TS-35 layer boilers to the combustion of Khara Norsk brown coal (Qrn = 2720 kcal/kg; Ap = 13.2%; Wр = 40%) in a fluidized bed.

The need for reconstruction was caused by the low efficiency of layer boilers and significant repair costs. In addition, the goal was to increase the boiler productivity to 42 t/h.

The reconstruction affected the following boiler components:

■ the profile of the lower part of the firebox has been changed. The chain grille has been removed, the front and rear screens have been extended downwards. The side walls are covered with heavy lining at a height from the air distribution grille to the axis of the cooling panels; the screens of the side walls remain unchanged;

■ removable air distribution caps are installed on the air distribution grille, ensuring uniform liquefaction of the layer, and two pipes for draining the layer, cooled with water, to remove slag;

■ to light the boiler, a kindling device is installed in a separate air box under the grate. Hot gases generated during the combustion of diesel fuel heat the layer from below and ensure ignition of the coal supplied to the furnace. After stable ignition of coal in the layer, the kindling device is turned off;

■ sharp blast nozzles are installed on the front and rear walls of the firebox. Air, preheated in the air heater, is supplied to the nozzles by a standard VD-13.5×1000 fan;

■ to ensure liquefaction of the layer, two VDN-8.5-I×3000 high-pressure fans were additionally installed;

■ the second superheater package along the gas flow, located in the rotary gas duct, has been enlarged;

■ the second air heater cube along the gas flow was dismantled;

■ the boiler economizer is increased by 3.5 loops;

■ the blades of the standard D-15.5 smoke exhauster were enlarged, and the engine was replaced with a more powerful one, which is associated with an increase in boiler productivity from 35 to 42 t/h.

The reconstructed furnace with FKS is fundamentally different from traditional fluidized bed furnaces, namely:

■ high liquefaction speed (up to 9-10 m/s), kakutopox CFB. Due to intensive mixing, there are no uneven temperatures and fuel concentrations over the layer area. The layer material is partially carried into the furnace volume and, being intensively cooled, flows down the back screen back into the layer, cooling it. Due to repeated intra-furnace circulation of the layer material, good combustion of combustibles is ensured;

■ only 50-60% of the air involved in combustion is supplied under the grate; the rest of the air is supplied through secondary blast nozzles. Lack of air in the layer leads to partial gasification of the fuel and two-stage combustion;

■ secondary air supplied through nozzles located on the front and rear walls of the furnace forms a powerful horizontal vortex, which contributes to the afterburning of gases and carried-out fines.

The applied technical solutions made it possible to significantly improve the boiler’s performance, in particular:

■ increase fuel burnout without the use of expensive separation devices and entrainment return used in CFB boilers. Maximum losses with mechanical underburning do not exceed 2.5%;

■ expand the temperature control limit of superheated steam due to intensified heat exchange in the furnace caused by a horizontal vortex;

■ regulate the layer temperature by changing the air flow under the grate without the use of submerged heating surfaces. When switching to gasification mode, the temperature of the layer decreases. The dependence of the layer temperature on the air flow rate under the grate has a clearly expressed maximum at the point of their stoichiometric ratio; with an increase or decrease in air in the layer, the temperature drops. Thanks to this, the boiler has no load restrictions due to the high bed temperature;

■ achieve moderate wear of convective surfaces, because 60-70% of the total entrainment is the slippage of relatively large particles (100-1000 microns) that did not fall into the horizontal vortex, the rest is very fine ash, which has little effect on wear;

■ reduce emissions of nitrogen oxides by 2 times (relative to layer and flare furnaces). Due to two-stage combustion and low bed temperatures throughout the entire control range of loads and with any excess air in the furnace, the maximum NOx concentration does not exceed 200 mg/m3;

■ exclude significant losses due to chemical underburning. The concentration of carbon monoxide due to afterburning in a vertical vortex does not exceed 100 ppm.

Comparative characteristics of the station No. 7 boiler before and after reconstruction are given in Table 1.

Table 1. Characteristics of the boiler Art. No. 7 Chitinskaya CHPP-2.

Parameter name	Meaning
Parameter name	Before reconstruction	After reconstruction
Productivity, t/h	35	42
Steam pressure, MPa	3,8	3,8
Steam temperature, °C	440	440
Feedwater temperature, °C	105	105
Heat loss with mechanical underburning, %	4,5	2,5
Gross boiler efficiency, %	82	86
Load control range, %	40-100	52-100
Excess air behind the firebox	1,4	1,3
Flue gas temperature, °C	175	180
CO concentration (no more), mg/m3	4000	100
NOX concentration (no more), mg/m3	450	200

The results of adjustment tests showed that the maximum steam output of the boiler after reconstruction is limited by the productivity of the smoke exhauster and amounts to 44 t/h. The filling of the furnace at loads above 35-38 t/h improves, the content of carbon monoxide in the gases decreases.

According to operating data, the combustion mode of the reconstructed boilers is characterized by high stability. Deviations in the temperature of superheated steam in stationary mode are short-term and do not exceed ±5 °C. Temperature imbalances across the width of the furnace and no pulsations are observed. The operating temperature of the layer is 820-980 °C.

During commissioning tests, it was revealed that the minimum thermal loads that ensure self-heating of the layer fully satisfy the specified boiler firing schedule. Coal consumption to maintain the minimum bed temperature is approximately 1.5 t/h, which is about 15% of fuel consumption for the boiler at rated load.

Ignition of the boiler begins with diesel fuel. After stable combustion of coal in the layer at a temperature of 500-550 °C, the pilot nozzle is turned off, the minimum fuel consumption is set, and heating of the boiler continues without outside interference in the combustion mode. Diesel fuel consumption for heating the layer during kindling from the cold reserve is no more than 200 liters. After the boiler has been idle for less than 6 hours, diesel fuel consumption is halved. When the boiler is idle for less than 3 hours, kindling is carried out without the use of liquid fuel, while the coal is ignited from the heat accumulated in the layer. Fuel oil can be used instead of diesel fuel.

Thus, as a result of the reconstruction, it was possible to obtain a more reliable and controllable boiler with a gross efficiency of at least 4% higher than before the reconstruction. The reliability, safety and environmental characteristics of the new firebox are not only on par with layer and torch fireboxes, but also superior to them.

To prevent abrasive wear of heating surfaces in contact with the fluidized bed, the technology of surfacing pipes with wear-resistant material was used at the Chita CHPP-2 (Fig. 1).

Considering the simplicity of the design and the possibility of burning any low-grade fuel, the new combustion device may be suitable for the design and reconstruction of pulverized coal and gas-oil boilers of low and medium power. Converting boilers to burning coal using this technology will not only save liquid fuel for kindling, but also eliminate the consumption of fuel oil for lighting the torch. The share of fuel oil used for these purposes can be reduced by an order of magnitude.

Example 2. Construction of a boiler house with three boilers with FKS furnaces. In 2003, the Amuragrocenter OJSC company built a boiler house with three KE-10-14-225S boilers for burning a mixture of brown coal (80%) and oat husks (20%) with FKS furnaces.

In Fig. Figure 2 shows the installation of equipment on pre-prepared foundations of building structures of the boiler building, which is a light metal frame with pre-fabricated sandwich-type wall panels. Experience in the construction of boiler houses of this design shows the possibility of reducing the full cycle of construction of boiler houses with a thermal capacity of 15-30 Gcal/h in 5-6 months, excluding stripping operations.

Example 3. Construction of a boiler house with three steam boilers for burning brown coal from the Itat deposit. In 2005, the management of OJSC Altaivagon (Rubtsovsk, Altai Territory) decided to build its own boiler house with three KE-25-14-225PS steam boilers (Fig. 3), dictated by economic considerations. As a result of construction, the enterprise received its own energy source, equipped with highly efficient boilers made using FKS technology, with an efficiency of 84-87%, burning cheap brown coal from the Itatskoe deposit (characteristics of coal for working mass: pH = 3100 kcal/kg; Wр = 39%; Ar =12%).

To increase the reliability and durability of the heating screen surfaces in the fluidized bed action zone, two methods were used to protect pipes from abrasive wear (Fig. 4). At a height of 1 m from the air distribution grille, cast iron linings (grade ChH16, hardness 400-450 HV, operating temperature up to 900 °C) are fixed on the pipes; at a height of 1 m from the linings, protection is applied by gas spraying of a layer of self-fluxing alloy PR-NH17SR4-40/100 ( thickness of the deposited layer - from 0.5 to 1.4 mm, hardness - 418 HV). As operating experience shows, this protection guarantees reliable operation of screen pipes.

The boiler diagram KE-25-14-225PS is shown in Fig. 5.

The boiler is equipped with an automatic control system that provides all standard adjustments, protections and alarms for low and medium power boilers. Provides start-up of the boiler from a cold state and a “hot” standby and operation of the boiler in automatic mode.

The boiler KE-25-14-225PS, in accordance with the requirements of SNiP and the operating technology of the furnace, is equipped with a measurement system that provides control and recording of the following parameters:

■ level (height) of the layer (control);

■ water level in the drum (water flow through the boiler) (control and registration);

■ steam pressure in the drum (water pressure at the inlet and outlet of the boiler) (control);

■ air pressure in the air distribution grille (control);

■ vacuum in the furnace (control);

■ vacuum at the smoke exhauster (control);

■ flue gas temperature (control);

■ layer temperature (control and registration);

■ temperature of combustion gases (control);

■ temperature of water leaving the boiler in hot water mode (control and registration);

■ steam consumption (control and registration).

The control and monitoring panel is shown in Fig. 6.

All automation systems are combined into one control circuit. The operator's workplace (boiler operator) is located in a separate room. It can simultaneously control several boilers and other process equipment.

Table 2. Results of testing the operation of the KE-25-14-225PS boiler st. No. 3 of the Altaivagon boiler house, Rubtsovsk.

Table 3. Results of industrial tests of boilers KV-F-11.63-115PS st. No. 1, 2 and 3 in the central boiler house of Borzya.

Characteristics	Art. No. 1		Art. No. 2		4,6	10,1	4,9	9,5	4,2	9,8
Water consumption, m3/h	218	218	210	210	200	200
CO concentration, mg/nm3 (a=1.4)	405	360	180	382	477	438
NOX concentration, mg/nm3 (oc=1.4)	347	353	235	409	297	207
Combustible content in entrainment, %	10	14,5	15,8	15,5	11,9	13
Air flow per layer, Nm3/h	7200	13410	6900	13760	8210	12940
Total air flow per boiler, Nm3/h	10000	20600	11000	22400	12000	20600
Fluidized bed temperature, °C	765	810	726	792	742	792
Gross boiler efficiency, %	89,9	84,4	86,3	84,3	84,6	83,5
Specific consumption of standard fuel, kg/Gcal	155,1	155,8	158,9	161,9	160,2	161,3

Note: fuel - brown coal: 0^=3012 kcal/kg; Ar=13.2%; Wp=35.9%.

Control and monitoring is carried out from a computer from a separate room via a network, or from a touch screen on the control panel. The boiler control panel view is shown in Fig. 7.

The test results of the KE-25-14-225PS boiler (Table 2) showed high efficiency, low emissions of NOx (300-385 mg/nm3) and CO (80-300 mg/nm3). The content of combustibles in the entrainment with increasing load from 30 to 100% changed in the range of 10-21% with a corresponding change in mechanical combustion from 1.59 to 3.87%. The boiler efficiency varied within the entire load range from 84.9 to 86.3%. The steam temperature was 204-225 °C. The temperature of the fluidized bed averaged 890 °C and ensured reliable slag-free operation of the boiler. The specific consumption of equivalent fuel was 188.3 kg/MW.

Example 4. Reconstruction of a boiler house by replacing worn-out boilers with two hot water boilers with FKS fireboxes. In 2005-2006 In the city of Mogocha, Trans-Baikal Territory, the housing and communal services boiler house was reconstructed by replacing worn-out boilers with two water-heating boilers KEV-10-95PS (Fig. 8) with FKS furnaces for burning Kharanorsky brown coal.

Main technical characteristics of the boiler:

■ heating capacity 6.98 MW (6 Gcal/h);

■ water pressure at the inlet is no more than 0.8 MPa (8.0 kgf/cm2);

■ water pressure at the outlet is not less than 0.24 MPa (2.4 kgf/cm2);

■ outlet water temperature no more than 95 °C;

■ boiler efficiency (gross) 85.87%;

■ total fuel consumption 2596 kg/h. A design feature of the boiler is the presence of an FKS firebox installed in the lower part of the boiler combustion chamber, formed by brick walls converging to the bottom. The FKS firebox consists of an air distribution grille (area - 2.4 m2) with an air box at the bottom, a kindling chamber with a nozzle, a layer drain pipe and a slag removal device. Removable cast iron caps are installed on the grille in a corridor order. Air is supplied under the grille from a high-pressure fan VDN 8.5×3000-I (17,000 m3/h; 75 kW).

The fuel preparation system provides coal with a particle size of up to 25-30 mm into the layer. Feeding is carried out into the layer by two PTL 600 feeders with dismantled rotors.

Before lighting the boiler, inert filler is loaded onto the air distribution grille. Sand, small crushed stone or slag of fractions 1-6 mm are used as inert filler. The height of the poured layer is 250-350 mm.

The boiler firing system includes a solar oil tank, a fuel pump, mechanical and fine filters, and fittings. The boiler is fired by heating the layer with hot gases supplied under the grate, formed during the combustion of liquid fuel in the ignition chamber. The temperature of the layer during kindling is controlled by changing the consumption of kindling fuel.

To reduce losses due to mechanical underburning, the boiler is equipped with a two-stage entrainment return system. The first stage operates by expanding the furnace upward, which makes it possible to separate the largest particles flying out of the layer. Along the inclined walls of the lower part of the furnace, the particles roll back into the volume of the fluidized bed. The second stage is the convective beam of the boiler. The flammable particles trapped in it are returned through pneumatic transport lines to the above-layer space.

The boiler has two-stage combustion. Part of the air (about 70%) enters under the air distribution grille. The remaining air is fed into the combustion chamber through sharp blast nozzles. Both primary and secondary air are supplied from one VDN 8.5×3000-I fan.

A smoke exhauster DN-12.5× 1500 (75 kW) is installed behind the boiler.

Currently, the installed boilers are in operation, the staff reviews are positive.

Example 5. Reconstruction of a central boiler house by installing three station boilers with an FKS firebox. In 2006, in the city of Borzya, the central boiler house was reconstructed with the installation of three new hot water boilers KV-F-11.63-115PS, station No. 1, 2 and 3. The boiler diagram is shown in Fig. 9.

Main design characteristics of the boiler:

■ heating capacity 11.63 MW (10 Gcal/h)

■ water pressure at the inlet no more than 1.0 MPa (10.1 kgf/cm2);

■ hydraulic resistance of the boiler unit is 0.18 MPa (1.8 kgf/cm2);

■ inlet water temperature is at least 70 °C;

■ outlet water temperature no more than 115 °C;

■ boiler plant efficiency (gross) 84%;

■ estimated fuel consumption (Kharanor brown coal) 4112 kg/h.

The results of industrial tests of new boilers are given in table. 3.

Example 6. Construction of a pilot industrial energy technology plant for the production of semi-coke from Berezovsky brown coal using an FKS reactor. In 2006, in the boiler house of OJSC Razrez Berezovsky 1, a pilot industrial energy-technological installation for the production of semi-coke from Berezovsky brown coal was put into operation (Qrn = 16168 kJ/kg, Ap = 2.93%, Wр = 34.1%) with maintaining the thermal power of the boiler.

The installation is designed on the basis of a serial water heating boiler KV-TS-20. A special feature of the installation is the use of an FKS reactor.

Coal from the bunker is fed into the fluidized bed through four chutes located at the front of the boiler. In the reactor at temperatures of 580-700 °C, its pyrolysis is carried out, accompanied by the combustion of volatiles and fines removed from the layer. Air is supplied under the reactor grate from a high-pressure fan VDN-8.5×3000.

From the reactor, the resulting charcoal is “overflowed” into a tubular cooler.

Cooled there to a temperature of 100-120 °C, it is transported to a storage hopper using a conveyor system.

As a result of thermochemical treatment of coal in a fluidized bed reactor, semi-coke is obtained (Qrn = 27251-27774 kJ/kg, Ap = 7.95-8.25%, Wр = 4.2-3.42%).

The weight yield of semi-coke is about 25% of the coal consumption supplied to the boiler.

The energy-technological installation operates with optimal ratios of primary and secondary air and supplied fuel, which allows, with minimal heat losses and harmful emissions for this design, to obtain 20 Gcal/h of heat and ensure a stable output of semi-coke of the required quality with good economic indicators. The estimated payback period for investment costs is no more than 17.5 months.

Work on the creation of powerful domestic boilers with CFB began in 1987 and was carried out by a large team of organizations: VTI, NPO TsKTI, SKB VTI, Sibenergomash PA, KazNIIenergetica, UPI, MPEI. Combustion of fuel in a CFB due to its low temperature (850 – 900 o C) ensures a reduction in the yield of nitrogen oxides, and when limestone is added, sulfur oxides are suppressed.

Limestone consumption is 3 - 6 kg per 1 ton of natural fuel or for a boiler with a steam capacity of 500 t/hour - 0.2 - 0.4 t/hour.

The amount of limestone can be reduced for fuels with a high content of alkaline earth compounds, for example, for coals of the Kansk-Achinsk basin, the mineral part of which contains up to 40% or more calcium and magnesium compounds.

Air is supplied by two fans. The primary blast fan supplies air through the grate into the firebox and into the pseudo-hydraulic seals. The secondary air fan supplies air to the firebox at three levels.

Boilers with CFB are made according to the same scheme: a combustion chamber with the heating surfaces of a superheater, cyclones and a remote convective flue in which the economizer and air heater are located in its upper part.

After the cyclones, the ash returns through the ash gate to the lower part of the combustion chamber. Solid particles of unburnt fuel are removed from the furnace and returned through cyclones back into the bed. Hot ash after the cyclone is sent to external ash coolers.

The primary ash collector is an impact type separator consisting of staggered U-shaped elements (channel separator) suspended from the boiler roof, which form a labyrinth in the path of gas and solid particles (Fig. 1.2). The first two rows of the ash collector are located in the firebox in front of the entrance to the horizontal flue. The ash caught in them is returned to the firebox along the rear wall. Solids collected by other rows of the separator (in the horizontal flue) are sent to the hopper and returned to the lower part of the firebox through four L-valves

Fig.1.2. Channel separator: 1 – gas and solid particles; 2 – solid particles returned to the furnace; 3 – solid particles returned to the storage bin

The latter serve to control the content of material in the firebox by regulating the bypass from the hopper to the firebox. The organization of two-stage primary separation with an in-furnace channel separator reduces the importance of the necessary external circulation of particles.

This type of firebox is used for boilers with thermal power from 20 to 500 MW. Within the framework of the federal program “Environmentally Clean Energy”, a project for the construction of a pilot industrial boiler with a CFB type E-220-9.8-540 AFS OJSC “Belenergomash” has been developed and is being implemented for burning AS at Nesvetai State District Power Plant. The boiler is designed for efficient combustion of low-reaction AS with Q nr = 4100 - 500 kcal/kg with an ash content of 40% and a sulfur content of up to 2%, without backlighting with fuel oil throughout the entire operating load range, with minimal emissions of pollutants into the atmosphere (reduction of sulfur emissions by 90 %, and NO x – no more than 300 mg/m3).

The fundamental advantage of the boiler is the possibility of its placement within the dimensions of an existing boiler cell without the use of expensive nitrogen and desulfurization systems.

Rice. 1.3. State district power station with CFB boilers of degraded quality:

1 – ash processing complex; 2 – coal and limestone farms; 3 – boiler with CFB; 4 – steam turbine; 5 – ash catcher; 6 – generator; 7 – smoke exhauster; 8 – chimney

The boiler is a prototype for the technical re-equipment of numerous Russian power plants that burn low-grade solid fuels with low reactivity, high content of ash, moisture, and sulfur. It is very important that in such a boiler it is possible to burn fuels of various types and quality, without significant changes in operational performance and with a significant improvement in environmental performance.

The boiler uses CFB technology with compact separators of the impact-inertial type (Fig. 1.2), which has been successfully used on a number of boilers from Babcock-Wilcox (USA).

Similar boilers have been developed for other thermal power plants: EP-250-16.8-545 BKFN for Moscow Region coal and Kuznetsk T-grade coal; E-170-9.8-540-DFN for peat (Fig. 1.3).

Introduction

To supply heat to the surface complex and to heat the shafts, Ukrainian mines use their own boiler houses, a significant number of which run on solid fuel. This is due to sufficient reserves of thermal coal, however, the share of deteriorated coal, with an ash content of up to 50%, in the total balance of solid fuel in the country is approaching 39% and, in the future, will increase due to the development of thin seams. When burning high-ash coals, the efficiency of coal boilers decreases, their heating capacity does not reach the design value, and as a result, the reliability of heat supply to consumers decreases.

One of the effective technologies for burning low-grade and high-ash (up to 80%) coals is the use of low-temperature fluidized bed (LTFL). This method of fuel combustion is characterized by a high level of mixing of fuel and oxidizer, increased residence time of fuel in the combustion zone compared to layered furnaces, intense heat removal to heating surfaces, the absence of moving parts in the combustion volume, the possibility of burning fuels of different composition and quality in one unit, reduced up to 1–5% fuel content in the layer. NTKS technology facilitates fuel ignition, prevents sintering of fuel particles and slagging of convective heating surfaces.

1. Relevance of the topic

Due to the increasing share of coal of deteriorated quality, with an ash content of up to 50%, associated with an increase in the number of thin seams in the country, the use of boiler plants with low-temperature fluidized beds capable of using this type of fuel is relevant.

Currently, control of a boiler unit with a low-temperature fluidized bed is carried out manually by the operator and is not always successful and, as a result, is accompanied by forced unproductive equipment downtime, and in the worst case, a complete stop of the technological process.

These boiler plants have been used in Ukraine for a long time. During the entire period, no improvements were made to facility automation systems. In the conditions of restructuring and transition to market mechanisms in the Ukrainian energy sector, the requirements for boiler plants are increasing. Unfortunately, outdated equipment is not capable of bringing the boiler unit to the required characteristics. It is necessary to modernize the boiler plant automation equipment.

2. Characteristics of the automation object

Fluidized bed combustion is one of the technologies for burning solid fuels in power boilers, in which a fluidized bed of fuel particles and non-combustible materials is created in the firebox. The technology was introduced into the energy sector from the chemical industry around the 1970s. .

Figure 1 – Methods of burning solid fuels
(animation: 4 frames, 20 loops, 26 kilobytes)

2.1 Combustion technologies

In an upward gas flow, a load of solid particles can be in three states:

at rest, when the gas velocity is low and it cannot lift particles - typical for layer furnaces;
in pneumatic transport mode, when particles are transferred with a fast gas flow - in chamber furnaces;
in a fluidized state at an intermediate gas velocity, when, when passing through the layer, it “spreads apart” the particles and increases its thickness, lowering the density, but is not able to carry the particle beyond the layer. This last mode is created in fluidized bed furnaces.

The fluidized bed can be high-temperature or low-temperature (800–900 °C); currently, for a number of reasons, the latter is almost always used. In particular, it very effectively suppresses the release of nitrogen oxides and it is possible to use an immersed surface to which the heat transfer coefficient is exceptionally high (heated fuel particles come into direct contact with it, and part of the heat is transferred not by convection, but by thermal conductivity). To adjust the temperature of the layer in order to avoid slagging, water and steam can be introduced, but in principle, due to the high abrasiveness of this layer, fireboxes using it are not prone to slagging.

A significant amount of inert fillers is introduced into the fluidized bed - slag, sand, dolomite, limestone; they increase heat transfer. Dolomite and limestone, in addition, bind up to 90% of sulfur oxides into carbonates. Fuel can be coal (including in the form of residues in the ash from low-efficiency boilers), oil shale, peat, wood and other waste.

Fluidized bed furnaces are not sensitive to the quality of the fuel in terms of its chemical composition, but are sensitive to the uniformity of the fractional composition of fuel particles and inert backfill. Combustion in these fireboxes is more intense than in conventional layer fireboxes, their dimensions are smaller; however, they require the creation of an air distribution grille and a fan of greater power. Other disadvantages of this type of firebox include:

removal of up to 20–30% of the total fuel carbon (therefore, these furnaces are recommended to be used when it is possible to burn out carryover of 0–1 mm in size in the working space of the boiler);
slagging of the internozzle space and the nozzles themselves of the air distribution grates with insufficient dynamic air pressure;
very high abrasive wear of heat transfer surfaces, especially high for submersible ones.

The effect of intense combustion, similar to that observed during combustion in a fluidized bed, can be obtained by constantly shaking the grate with pieces of fuel of any size; but due to the reduction in the strength of the grate metal at high temperatures, this method is difficult to implement in practice.

Fluidized bed furnaces under pressure up to 16 kgf/cm² with deep purification of gas from ash can be used to organize the operation of gas turbines using solid fuel (as part of a high-pressure steam generator PGU)

2.2 Description of NTKS technology

In recent years, there has been increased interest in boilers equipped with fluidized or fluidized bed furnaces (Figure 2). These furnaces occupy an intermediate position between layer combustion furnaces and flare furnaces. What they have in common with layer fireboxes is, first of all, the possibility of burning crushed material with pieces up to 10–20 mm in size and the presence of a grate through which air is supplied to the layer. As the speed of air blown through the layer increases, a moment comes when the aerodynamic force acting on each fuel particle overcomes the forces of mutual friction of the particles. A further increase in air flow leads to pseudo-liquefaction of fuel particles, the layer seems to boil (hence the name fluidized bed), its height and porosity increases.

The minimum speed at which pseudo-liquefaction begins is called the first critical speed Wcr1; at the second critical speed Wcr2, the aerodynamic force becomes equal to the gravitational force of fuel particles, and their intensive removal from the layer begins. Both of these parameters have strictly defined values only for a monodisperse material with a constant density, and the layer, as is known, consists of polyfractional inert material and fuel particles of different densities.

Real combustion devices with a fluidized bed operate at speeds from Wcr1 to Wcr2. There are furnaces with a regular or stationary fluidized bed (when the speed in it is close to Wcr1) and furnaces with a circulating fluidized bed (when the speed is close to Wcr2). In the latter case, a significant part of the unburned fuel is removed from the layer, which is then captured in hot cyclones and returned for burning.

It is important to note that in fluidized bed furnaces the amount of combustible material is usually a small fraction of the mass of the bed; it is based on inert material or fuel ash (when burning high-ash coals). Intensive mixing of solid particles under the influence of liquefying air passing through a layer of granular material provides increased heat and mass transfer in the layer. Immersion of heating surfaces in a fluidized layer allows the temperature to be maintained at a level at which the layer does not become slagged.

Figure 2 - Diagram of a boiler with a stationary fluidized bed at atmospheric pressure:
1 – steam generating panels; 2 – membrane screen; 3 – cyclone; 4 – filter; 5 – chimney; 7 – coal; 8 – limestone; 9 – solid particles from the cyclone; 10 – transporting air; 11 – combustion air; 12 – removal of slag; 13 – fluidized bed.

The main advantages of the method of burning solid fuel in a fluidized bed include the following:

a high heat transfer coefficient is ensured;
prolonged residence of particles in the layer allows the combustion of coal with high ash content and production waste;
it becomes possible to create a more compact combustion device without a dust preparation system, while the specific capital costs for the construction of a boiler house, as well as repair costs, are reduced;
the addition of limestone to the layer binds fuel sulfur with the ash residue, which reduces emissions of sulfur dioxide with flue gases into the atmosphere;
low temperatures in the layer (800–950°C) ensure the absence of thermal nitrogen oxides, which in some cases reduces emissions of nitrogen oxides into the atmosphere.

Extensive experience in using fluidized bed combustion devices in the energy sector has been accumulated in Germany, the USA, Finland and some other countries. In recent years, much attention has been paid to circulating fluidized bed furnaces. These boilers are distinguished primarily by the presence of cyclones, in which large particles removed from the layer are captured (Figure 3). The thermal cross-sectional voltage in such furnaces reaches 4–8 MW/sq.m, and the velocity of gases in the layer is 3–8 m/s. Similar parameters for furnaces with a stationary fluidized bed are respectively 2 MW/sq.m. and 1–2.5 m/s. Furnaces with a circulating fluidized bed have a higher degree of fuel burnout (approximately 99% versus 90–95% for boilers with a stationary fluidized bed), they can operate with a lower excess air ratio (1.1–1.15 instead of 1.2–1 ,25).

The fuel supply system of circulating fluidized bed boilers is simpler, they are less demanding on fuel quality and are better adapted to its staged combustion, which is necessary to reduce nitrogen oxide emissions. Such furnaces make it possible to bind more than 90% of sulfur at a molar ratio of Ca/S = 2, while in furnaces with a stationary fluidized bed, more limestone (Ca/S = 3) is required to bind 80–90% of sulfur.

The largest circulating fluidized bed boiler in Europe was built by Zurgi in Duisburg (Germany). By mid-1987, it had worked about 10 thousand hours. The boiler's steam capacity is 270 t/h, fresh steam pressure is 14.5 MPa, superheat temperature is 535°C.

Figure 3 - Diagram of a boiler with a circulating fluidized bed at atmospheric pressure:
1 – coal and lime; 2 – secondary air; 3 – fluidized bed reactor; 4 – evaporation part; 5 – cyclone; 6, 11 – steam boilers; 7 – electric precipitator; 8 – air heater; 9 – chimney; 10 – ash; 12 – material cooler; 13 – air; 14 – primary air.

Recently, research into pressurized fluidized bed furnaces has expanded significantly (Figure 4). The main advantage of such furnaces is the possibility of implementing a combined cycle, when the steam generated in the boiler is used in a steam turbine, and the high-pressure combustion products are used in a gas turbine. At the same time, the thermodynamic efficiency of the cycle increases, the overall dimensions of combustion devices are liquefied to an even greater extent (by almost 60% compared to conventional boilers) and harmful emissions into the atmosphere are reduced.

The widespread introduction of boilers with pressurized fluidized bed furnaces is hampered by the fact that there are still a number of unresolved problems. For example, combustion products used in a gas turbine require careful cleaning. Fabric filters cannot be used in this case due to the high temperature of the gases, and mechanical ash collectors do not provide the required degree of gas purification. The second unresolved problem is ensuring the density of the installation operating under pressure up to 1.4 MPa.

Figure 4 – Schematic diagram of an installation with a fluidized bed under pressure:
1 – gas turbine unit; 2 – exhaust gases; 3 – cyclone; 4 – ash; 5 – chamber with a fluidized bed under pressure; 6 – steam turbine unit; 7 – coal and lime; 8 – air.

Back in 1976, the energy company American Electric Power announced the construction of a 170 MW demonstration power unit with a pressurized fluidized bed furnace. Preliminary tests were carried out at a dense installation in Leasenhead (UK). They confirmed that emissions of sulfur dioxide and nitrogen oxides are significantly reduced, and the performance of the blade apparatus of gas turbine plants and combustion products is increased.

2.3 Automation of boiler units

Monitoring the progress of the heating process, along with the implementation of emergency blocking tasks, ensures that the technical regime is maintained in strict accordance with the norms of the technological regulations. Solving these problems completely eliminates the shutdown of boilers due to uncontrolled violations of the boundaries of technological regulations, and also dramatically increases the safety of operation of all technological systems.

Figure 5 – Block diagram of regulating the parameters of a boiler equipped with a low-temperature fluidized bed firebox:
1 – blower fan; 2 – MEO executive mechanism; 3 – fuel thrower; 4 – boiler; 5 – direct-flow cyclone; 6 – economizer; 7 – cyclones of the first and second stages of flue gas purification;
8 – smoke exhauster; 9 – make-up pipeline; 10, 11, 12, 13, 14 – regulators for vacuum, level, slag release, air and fuel flow, respectively.

The block diagram of automation of boiler units (Figure 5) provides for the following activities:

1. Control of tracking parameters:

flue gas temperature;
blast air pressure;
vacuum in the furnace of the boiler unit;
air temperature during ignition;
temperature in the layer;
hot water temperature or steam pressure in the boiler drum;
hot water or steam consumption;
blower motor current;
smoke exhaust motor current;
pressure before and after liquid fuel;
gas temperature in front of the economizer and smoke exhauster;
water pressure in front of immersed heating surfaces;
hot water pressure after the boiler;
vacuum in front of the economizer, cyclone, smoke exhauster;
oxygen content in flue gases;
fluidized bed level;
water level in the boiler drum (for steam boilers).

2. Alarm and protection:

blast air pressure is low;
the vacuum in the furnace is low;
the temperature in the layer is high or low;
lack of water flow through the boiler;
steam pressure is high;
water temperature is high;
emergency level in the boiler drum;
ignition temperature is high;
lack of flame when igniting the boiler unit.

3. Remote control of boiler mechanisms:

smoke exhauster - remotely;
blower fan - remotely interlocked with a smoke exhauster and a boiler protection circuit;
entrainment return fan No. 1 and No. 2 – remote interlocked with the blower fan;
coal thrower - remotely interlocked with a blower fan and a boiler protection circuit;
liquid fuel supply pump - remote and local with flame control depending on the number of ignition nozzles;
ash unloader;
vibrator;
ash removal conveyor;
unloader of captured particles from the first stage of gas purification.

4. Automatic regulation

Conclusions

Increasing energy prices, a shortage of domestic fuel resources, a decrease in the quality of coal, and increasing requirements for reducing environmental pollution require the introduction of a more advanced method of coal combustion into production.

It is the availability of fuel and energy resources that determine the pace and scale of development of individual areas of industrial and agricultural production. The main objectives are to ensure more comprehensive processing of raw materials, the creation of resource-saving equipment and technologies, and a sharp reduction in losses and waste. In recent years, in many countries, the restructuring of the fuel balance in order to reduce dependence on oil and gas has revived interest in coal issues.

When writing this essay, the master's qualification work was not completed. Date of final completion of the work: December 15, 2012. The full text of the work and materials on the topic of the work can be obtained from the author or his supervisor after the specified date.

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