RU2255962C1 - Process of producing water-coal fuel for combustion in gas-mazut boiler - Google Patents

Abstract

FIELD: alternate fuels.

SUBSTANCE: invention aims at transferring gas-mazut boilers consuming natural gas or mazut to combustion of water-coal fuel prepared from fuel. Process of invention comprises gravitational concentration of coal, crushing and wet grinding of coal to average surface area of particles belonging to disperse phase not higher than 3 μm. Preliminarily, moisture content, ash level, chemical analysis of ashes, slag-forming temperature of ashes, and combustion heat of water-coal fuel are determined from condition (i) that such amount of combustion products is formed in boiler, which provides achievement of a combustion products' velocity in furnace space of boiler exceeding critical velocity, at which ash particles precipitate, and (ii) that temperature of the water-coal fuel combustion products in boiler furnace outlet is not above slag-forming temperature of ashes. Gravitational concentration of coal is performed before grinding thereof and moisture content, ash level, chemical analysis of ashes, slag-forming temperature of ashes, and combustion heat of water-coal fuel are controlled according to preliminarily made computations.

EFFECT: simplified and reduced in price fuel production process, eliminated precipitation of ashes in furnace space of boiler, and lack of elevated pollution of heating surfaces.

2 cl, 3 ex

Description

The invention relates to energy and can be used in the conversion of gas-oil boilers from natural gas or fuel oil to the burning of coal-water fuel (WUT), prepared from high-ash coals.

In gas-oil boilers, steam formation and superheating of steam occurs in a system of tubular heat exchangers, mainly (more than 90%) due to radiant heat transfer.

In the combustion products of natural gas or fuel oil, the amount of ash particles is negligible. Their interaction with the surface of the heat exchangers occurs in the zone of convective heat transfer, that is, in the region of relatively low temperatures, in which the ash becomes solid. Due to this, in gas-oil boilers there is practically no loss of ash in the furnace volume and its adhesion to the heating surface.

When transferring gas-oil boilers to the ash VUT, it is necessary to preserve the total amount of heat transferred to the heated medium, to prevent precipitation of the ASU ash particles in the furnace volume, their accumulation in stagnant zones and sticking to heat-exchange surfaces.

Among the requirements for fuel oil, it is indicated that the ash content of fuel oil should not exceed 0.3%, humidity - 2%, and the calorific value of the dehydrated mass, on average, is 40 MJ / kg (Vergazov BC Design and operation of boilers: Questions and Answers: Handbook. 1991, p. 49). In this regard, in the preparation of HLF intended for burning in gas-oil boilers, the main attention is paid to the need to reduce the ash content of HLF for the reasons mentioned above, and to increase the mass content of the solid phase in HLW, which is equivalent to the condition for increasing the heat of combustion of HLW.

With the prevailing approach to the problem of converting gas-oil boilers to HLW, they seek to obtain fuel with the lowest possible, for economic reasons, ash content and maximum heat of combustion. In some cases, these requirements are contradictory or cause additional costs. For example, with a decrease in the ash content of the initial coal, in order to maintain an acceptable viscosity and stability of the HFC, special chemical additives become necessary, which increases the cost of the HFC. Thus, in fact, the goal is to get fuel with a consistency close to fuel oil, the use of which is cost-effective due to the relatively low cost of coal compared to the cost of regular fuel.

A known method for the preparation of HLF for combustion in gas-oil boilers with a mass concentration of solid phase above 50%, ash content on a dry mass of coal less than 3%, with a content of particles less than 200 microns in size 99.5%, softening temperature of ash above 1316 ° C (1589 K) and heat of combustion above 15 MJ / kg. The tests showed that when burning low-ash HLW, there is no increased contamination of the heating surfaces with ash and increased erosive wear (due to the possible abrasive effect of the same ash particles). Based on this, it was concluded that gas-oil boilers can be converted to VUT produced from coal with low ash content (less than 3%) without any significant modifications to the steam boiler itself (with the exception of fuel nozzles made from erosion-resistant ceramics) (Demonstration of coal / water -mixture (CWS) combustion. Power. 1991. V. 135, No. 10, p. 114; Miller BG, Scaroni AW The Pennsylvania State Universit's Superclean Coal-Water Slurry Demonstration Program. Proceedings of the 15 International Conference on Coal & Slurry Technologies April 1990, Clearwater, USA).

The disadvantage of this method is the need for its implementation, the organization of mass production of concentrated (more than 50% by weight) HLF of a high degree of demineralization (less than 3%), which in itself is a difficult technical problem when using coal with an initial ordinary ash content of 12-20%, leading to a sharp increase in the cost of the fuel and energy complex. Reducing the ash content of coal to 7-10% is easily achieved by technically effective, cheap methods of gravitational enrichment. For the subsequent reduction of coal ash to less than 3%, it is necessary to use flotation enrichment methods with refining, requiring the use of special chemicals, which dramatically complicates and increases the cost of the technology as a whole. In the case of brown coal, which, as a rule, is poorly floated, to achieve the required ash content, methods are used for chemical removal of the ash portion of coal. In addition, the problem of the disposal of demineralization waste generated during the production of HLW, the volume of which is about 25-35% of the production of demineralized HLW, should be solved.

There is also a known method of preparing a fuel-grade chemical fuel for burning with a mass concentration of solid phase up to 56.0-61.5%, with ash content of coal on a dry mass of 7-18% and with a dispersion of solid phase "-250 microns", followed by the supply of chemical-grade fuel to the boiler ( TPE-214, steam capacity 670 t / h), in which simultaneous or separate burning of natural gas, fuel oil and pulverized coal is possible. The tests showed that the joint or separate combustion of fuel-grade coal in a gas-oil-coal-fired boiler occurs without any complicating factors (slagging of convective heating surfaces, their erosion wear under the influence of ash particles, etc.) (Ercolani D., Minnetti G., Belykh BN and others. The try-out of coal water suspension preparation, transportation and combustion technology on the Belovo to Novosibirsk coal pipeline. Proceedings of the 16 international conference of coal & slurry. April, 1991, Clearwater, Florida, USA , p.1-9).

The disadvantage of this method is that when burning HLF of this composition in gas-oil boilers, ash will fall on the underneath of the boiler and slagging of convective heating surfaces is possible (depending on the chemical composition of the ash). For these reasons, the direct use of HLW of the indicated ash and humidity for combustion in gas-oil boilers becomes technically impossible.

The closest technical solution (prototype) is a known method of preparing water-coal fuel for burning in a gas-oil boiler, including gravitational enrichment of the source coal, crushing of the source coal, its wet grinding to colloidal particle size to obtain a water-coal suspension with an average surface size of the dispersed phase of not more than 3 μm , dilution of the resulting suspension with water to a concentration of 1-3%, stepwise demineralization of crushed coal to reduce its ash content with the formation of first primary and secondary products, their subsequent joint demineralization by combining products with similar ash levels and dehydration to obtain HLW with a solid phase ash of 0.5-2.0% (RF Patent No. 2178455, class C 10 L 1/31, 2000 g.).

The disadvantage of this method is that it is not effective (on a large source coal) using the gravitational concentration method to reduce the ash content of coal. Very complex, from the point of view of implementation and regulation, is the proposed technological scheme of flotation enrichment, as well as high costs for the disposal of high-ash demineralization waste, which must be taken into account when assessing the overall economic efficiency of the method.

The aim of the invention is to simplify and reduce the cost of the preparation of water-coal fuel for burning it in a gas-oil boiler, ensuring the absence of ash in the furnace volume of the boiler formed during the combustion of fuel oil, and the absence of increased contamination of the heating surfaces.

This goal is achieved by the fact that in the method of preparing water-coal fuel for burning in a gas-oil boiler, including gravity enrichment of coal, crushing coal, wet grinding of coal to a particle size with an average surface size of the dispersed phase of not more than 3 μm, in contrast to the prototype, previously calculated determine the humidity, ash content, chemical composition of the ash, ash slag temperature and the calorific value of water-carbon fuel, based on the conditions for the formation of such an amount of combustion products in the boiler, which The second one ensures that the rate of combustion products in the boiler’s furnace volume is above the critical speed at which ash particles precipitate and the conditions that the temperature of the combustion products of water-carbon fuel at the outlet of the boiler furnace should not exceed the ash slagging temperature, gravity enrichment of coal is carried out before grinding and regulate the humidity, ash content, chemical composition of the ash, ash slagging temperature and the calorific value of coal-water fuel in accordance with preliminary calculations.

The method differs in that when the temperature of the combustion products at the outlet of the boiler furnace is increased, it is reduced by changing the chemical composition of the ash of coal-water fuel due to the introduction of mineral additives, which use refractory metal oxides, for example, SiO ₂ .

The use of VUT in gas-oil boilers, prepared by regulating the moisture, ash, and chemical composition of ash, as well as gravitational enrichment of crushed coal, simplifies the technology for producing VUT and reduces the cost of its preparation.

Gravitational enrichment of crushed coal allows you to most completely remove heavy mineral impurities from it, which when burning HLW in the boiler form settling ash particles. When gravitational enrichment of crushed coal to a size of 1-5 mm of coal creates optimal conditions for the removal of mineral impurities with a density of more than 2500 kg / m ³

To prevent settling of ash particles (agglomerates) in the boiler, the size of which can reach 500 microns, which corresponds to the maximum size of the sprayed droplets, the amount of combustion products generated during the combustion of coal-water fuel should be such that the speed of movement of the combustion products anywhere in the furnace volume and gas ducts exceed the critical speed at which ash particles can settle.

The minimum flue gas velocity V _d at any point of the boiler must exceed a certain critical velocity V _cr for the largest particles. The value of the flue gas velocities at any section or point of the boiler is determined by the normative method (Aerodynamic calculation of boiler plants (normative method), third edition, edited by S.I. Mochan, Energy, Leningrad, 1977).

The critical gas flow rate at which ash particles do not settle in the boiler is calculated according to the empirical formula (Drying in the conditions of pneumatic transport, - Mushtaev V.I., Ulyanov V.M., Timonin A.S., M., Chemistry, 1984, 103 s.):

where a is a coefficient depending on the particle size (a≈12); ρ _m - bulk density of ash particles; B is a coefficient depending on the bulk properties of ash particles (B≈2 · 10 ⁵ ); L is the characteristic size.

It should be noted that due to the low bulk density of ash agglomerates of 0.3-0.5 g / cm ³ and increased, compared with the case of burning one of the standard fuels (natural gas or fuel oil), the formation of combustion products VUT, sedimentation of ash agglomerates in the boiler and boiler flues is unlikely. Calculations show that, in any section of the boiler, the speed of movement of the combustion products of the fuel-and-fuel assembly is, as a rule, significantly higher than the critical speed at which precipitation of ash agglomerates is possible. For example, in the case of the DKVR-4/13 boiler, a calculation using dependence (1) shows that for ash particles with the indicated characteristics, the critical velocity is in the range 0.2-0.8 m / s, and the calculated value of the product velocity the combustion of the fuel-and-chemical assembly along the boiler path is in the range from 1.5 m / s (under the boiler) to 12 m / s (diffuser).

To prevent sticking of ash particles on the heating surface, the temperature of the combustion products of the VUT at the outlet of the boiler furnace (T _t ) should not be higher than the slag temperature (T _W ) of the ash.

The temperature of the combustion products at the outlet of the boiler furnace (T _t ) is determined by the normative method (Thermal calculation of boilers (normative method). Edited by S.I. Movchan, A.A. Abryutin, G. M. Kagan and BC Nazarenko, St. Petersburg, 1998).

Other things being equal, the temperature at the outlet of the furnace depends on the ash content of coal, the chemical composition of the ash, and the moisture content of the fuel. The maximum permissible temperature of the combustion products at the outlet of the boiler furnace, at which there is no slagging of the semi-radiation heating surfaces, should not exceed the slag temperature (T _W ), which is determined by the empirical formula:

является показателем шлакования топлива

. Величина П_x.c.=1-0,025 (∑К/∑О) характеризует валовой состав золы. Здесь ∑К=Аl₂O₃+SiO₂+TiO₂ - кислотные компоненты золы, с высокой температурой плавления, ∑O=СаО+MgO+K₂O+Na₂O - основные компоненты золы, с более низкой температурой плавления. Показатель П_Fе учитывает влияние железосодержащих частиц и, в зависимости от пиритного или общего содержания серы S в пересчете на зольность: П_Fе=1-C₁/S при S>C₁; П_Fе=0 при S≤С₁ где C₁=0,8 при S=

=100

, % или C₁=0,485 при S=

=(100-A_d)

/A^d, %. Показатель П_Na характеризует влияние щелочных металлов: П_Na=К(Nа₃О)^m - 0,333, где К=0,576 и m=0,423 при использовании сведений об общем весовом содержании натрия в золе и К=0,693 и m=0,313 при учете содержания в золе водорастворимого натрия. Здесь

- общее содержание серы в золе,

- содержание пиритной серы в золе,

- общее содержание серы в угле на сухое состояние,

- содержание пиритной серы в угле на сухое беззольное состояние, А^d - зольность угля на сухое состояние (Алехнович А.Н., Богомолов В.В. Выбор температуры газов на выходе из топки по условиям шлакования. Журн. Теплоэнергетика, №8, 1994 г., с.25, 26).where is the value

is an indicator of fuel slagging

. The value of P _xc = 1-0.025 (∑К / ∑О) characterizes the gross composition of ash. Here ∑К = Al ₂ O ₃ + SiO ₂ + TiO ₂ are the acid components of the ash, with a high melting point, ∑O = CaO + MgO + K ₂ O + Na ₂ O are the main components of the ash, with a lower melting point. Index П _Фе takes into account the effect of iron-containing particles and, depending on the pyrite or total sulfur content S in terms of ash content: П _Fe = 1-C ₁ / S at S> C ₁ ; P _Fe = 0 at S≤C ₁ where C ₁ = 0.8 at S =

= 100

,% or C ₁ = 0.485 at S =

= (100-A _d )

/ A ^d ,%. The indicator P _Na characterizes the influence of alkali metals: P _Na = K (Na ₃ O) ^m - 0.333, where K = 0.576 and m = 0.423 when using information about the total weight content of sodium in ash and K = 0.693 and m = 0.313 when taking into account the content in ash of water-soluble sodium. Here

- total sulfur content in ash,

- pyrite sulfur content in ash,

- total sulfur content of coal in the dry state,

- the content of pyrite sulfur in coal for a dry ashless state, And ^d is the ash content of coal for a dry state (Alekhnovich A.N., Bogomolov V.V. Choice of gas temperature at the outlet of the furnace according to the conditions of slagging. Zhurn. Thermal engineering, No. 8, 1994 city, p.25, 26).

Since the slagging temperature depends on the composition of the mineral part of coal, then, as follows from formula (2), an increase in the proportion of components with a high melting point leads to an increase in the slagging temperature (T _W ).

It should be noted that a decrease (increase) in the temperature of combustion products only due to one of the regulated factors - ash content, chemical composition of ash or moisture is ineffective for the following reason. From calculations performed by the normative method, it follows that the same decrease (increase) in temperature at the outlet of the furnace is achieved by increasing (decreasing) the amount of the mineral part by 1.5-3 times higher (low) than when increasing (lowering) the content water. However, the additional heat loss during the emission of combustion products with water additives is approximately an order of magnitude or more, higher than the heat loss during the release of additional ash products. Therefore, the specific choice of the composition of the HLW, by calculating and regulating the ash, chemical composition of ash or moisture, ensuring the absence of slag formation in each case, is determined on the basis of the conditions for ensuring the rated load of the power plant while ensuring the technological possibility of obtaining the HLW of a given composition and overall economic efficiency.

If necessary, in order to maintain the nominal load of the boiler, the temperature of the combustion products in the boiler furnace can be increased due to the additional supply of natural gas or fuel oil to the boiler.

The following options for the implementation of the proposed method.

The first embodiment of the method.

Studies are carried out on the enrichment of coal crushed to a particle size of 1-5 mm by the gravitational method in order to determine the patterns of change in the chemical composition of ash from the ash value and determine the parameters of the beneficiation process.

According to regulatory methods, thermal and aerodynamic calculations of a given boiler unit are carried out when working on high-voltage fuel for coal of a given brand with an initial ash content of A ^d and for a number of both lower and higher ash values (the chemical composition of the ash in this case is taken on the basis of extrapolation of the chemical composition ash from the ash obtained in the study of the enrichment of the source coal), for example with a step of 2%, and various moisture values of VUT-w, in the range of 30-65%, for example with a step of 5%.

By the formula (1), the critical speeds are found. According to the formula (2) for each composition of the HUT, the value of the slagging temperature T _W ash is determined.

Based on the calculations, the boundary values are determined for ash content (A ^d ), chemical composition of ash and humidity (w) of the WCF, at which the rates of flue gases at various points of the boiler are higher than the corresponding critical ones, and the temperature of the products of combustion of the WCF at the outlet of the boiler furnace T _{t is} less or equal to the corresponding value of the slag temperature T _W

For the thus-calculated design compositions of the fuel-and-fuel mixture, their experimental testing is carried out, which consists in creating samples of the fuel-oil mixture with the specified moisture, ash and chemical composition of the ash, provided that the effective viscosity of the coal-water fuel ensures its high-quality atomization in a gas-oil boiler. As a result, the specific compositions of the fuel-chemical compound are determined, which can be practically implemented. If the number of possible HLF compositions is more than one, then the final choice of a specific technology for producing HLF, ceteris paribus (boiler efficiency, specific fuel consumption, etc.), is determined from the conditions for the implementation of the most economically efficient technology.

The second embodiment of the method,

измельчают до заданного гранулометрического состава и приготавливают ВУТ с минимально возможной влажностью w, соответствующей величине максимально допустимой вязкости μ₀.Coal with original ash

crushed to a predetermined particle size distribution and VUT is prepared with the lowest possible humidity w, corresponding to the maximum permissible viscosity μ ₀ .

For a given composition of high-temperature fuel assembly and a given coefficient of excess air α _{0, the} temperature at the outlet of the furnace T _{t is} calculated and compared with the temperature T _w , which depends on the chemical composition of the ash, which is calculated by the formula (2).

If T _W > T _t , then the temperature of the combustion products at the outlet of the furnace can be increased. If T _W <T _t , then the temperature of the combustion products must be lowered.

и w_i рассчитывают значения температур на выходе из топки котла Т_тi. Из сравнения величин Т_тi и Т_ш определяют значения

и w_i при которых температуры Т_тi и Т_ш примерно равны (температура Т_ш превышает Т_тi примерно на 10°С). Сжигание ВУТ такого состава в газомазутном котле происходит без образования золошлаковых отложений.In the first case, the temperature of the combustion products is increased by reducing the ash content of the source coal. In this case, while maintaining the viscosity of the WCF constant and equal to μ _0, while reducing the ash content of the WCF, its moisture content simultaneously decreases, i.e., w <w ₀ . At the same time, the requirement for exceeding the speed of the flue gas of a critical value should be maintained. For each ash value A ^d and the chemical composition of the ash, the corresponding humidity value is selected empirically, provided that the viscosity of the finished HLF remains constant μ ₀ . For each pair of values

and w _i calculate the temperature values at the outlet of the boiler furnace T _Ti . From a comparison of the values of T _ti and T _W determine the values

and w _i at which the temperatures T _Ti and T _{W are} approximately equal (the temperature T _W exceeds T _{Ti by} approximately 10 ° C). Combustion of such a composition in a gas-oil boiler occurs without the formation of ash and slag deposits.

и w_i рассчитывают значения температур на выходе из топки котла Т_тi и скоростей по тракту котла. Из сравнения величин Т_тi и Т_ш определяют значения

и w_i; при которых температуры Т_тi и Т_ш примерно равны (температура Т_ш превышает Т_тi примерно на 10°С). Проверяется отсутствие условия для выпадения золы в котле и газоходу котла. Этот состав ВУТ сжигают в газомазутном котле без образования золошлаковых отложений.In the second case, the necessary decrease in the temperature of the combustion products is achieved by increasing the moisture, ash content and chemical composition of the ash, provided that the viscosity μ ₀ VUT remains constant. The requirement of exceeding the speed of the flue gas of a critical value also remains. In this case, while maintaining the viscosity constant, with an increase in the ash content of the WCF, its moisture content simultaneously increases. For each ash value, the corresponding humidity value is selected empirically, provided that the viscosity of the finished HLF remains constant μ ₀ . For each pair of values

and w _i calculate the values of the temperatures at the exit from the furnace of the boiler T _ti and speeds along the path of the boiler. From a comparison of the values of T _ti and T _W determine the values

and w _i ; at which the temperatures T _Ti and T _{W are} approximately equal (the temperature T _W exceeds T _{Ti by} approximately 10 ° C). It is checked that there is no condition for ash loss in the boiler and the boiler flue. This WUT composition is burned in a gas-oil boiler without the formation of ash and slag deposits.

Implementation examples.

Example 1

The gas-oil boiler DKVR-4/13 is transferred to the combustion of fuel oil from coal of the GZhO brand. Coal has the following initial characteristics:

=28,13 МДж/кг,

=23,5%.

= 28.13 MJ / kg,

= 23.5%.

Chemical composition of ash:

SiO ₂ = 0.62, Al ₂ O ₃ = 0.20, Fe ₂ O ₃ = 0.10, CaO = 0.03, MgO = 0.03, K = 0.01.

=11,1 МДж/кг, w₀=40% и вязкостью μ₀=0,5 Па·с.Calculations show that from coal with the initial ash content it is possible to obtain VUT with

= 11.1 MJ / kg, w ₀ = 40% and viscosity μ ₀ = 0.5 Pa · s.

The aerodynamic calculation of the boiler and the calculations by formula (1) show that the volume of the flue gases generated satisfies the condition for exceeding the critical velocities for ash particles.

Calculations by the formula (2) give the value of T _W = 1111 ° C.

The thermotechnical calculation of the boiler, performed according to the standard method, gives the value of T _t = 1060 ° C.

Since T _W > T _t , direct combustion of HLW without slag formation is possible. At the same time, it is possible to increase the temperature T _t to the level of T _W , which will reduce fuel consumption by increasing the thermal characteristics of the fuel-and-chemical assembly.

при сохранении вязкости μ₀=0>5 Па·с и уменьшилась разница в значениях температур Т_ш и Т_т.It is advisable to change the composition of the VUT so that the heat of combustion increases

while maintaining the viscosity μ ₀ = 0> 5 Pa · s and the difference in temperature values T _W and T _t decreased.

Calculations show that it is possible to obtain a HLF of the following composition: Q = 15.01 MJ / kg, A ^d = 4%, w ^r = 40%, which provides a temperature T _t = 1068 ° C, which is lower than the temperature T _w = 1087 ° C . The volume of flue gases generated satisfies the condition for exceeding critical velocities for ash particles.

The preparation of HF includes gravity enrichment of coal crushed to minus 3 mm to an ash content of A ^d = 4%, grinding the coal to size with an average surface diameter of the solid phase of “-3 μm” and thickening the crushed coal to a moisture content of 40%.

In this example, the regulation of ash and chemical composition of the ash is carried out due to the gravitational enrichment of crushed coal.

Example 2

Gas-oil boiler DKVR-4/13 is transferred to the combustion of fuel oil from brown coal grade B2. Coal has the following initial characteristics:

=28,13 МДж/кг,

=17%.

= 28.13 MJ / kg,

= 17%.

Chemical composition of ash:

SiO ₂ = 0.56, Al ₂ O ₃ = 0.12, Fe ₂ O ₃ = 0.12, CaO = 0.13, MgO = 0.04, K ₂ O = 0.01, Na ₂ O = 0.01, TiO ₂ = 0.01.

=8,89 МДж/кг, w₀=56% и вязкостью μ₀==0,45 Па·с.Calculations show that from coal with the initial ash content it is possible to obtain VUT with

= 8.89 MJ / kg, w ₀ = 56% and viscosity μ ₀ == 0.45 Pa · s.

The aerodynamic calculation of the boiler and the calculations by formula (1) show that the volume of the flue gases generated satisfies the condition for exceeding the critical velocities for ash particles.

Calculations by the formula (2) give the value of T _W = 1073 ° C.

The thermotechnical calculation of the boiler, performed according to the standard method, gives the value of T _t = 1021 ° C.

Since T _W > T _t , it is possible to burn HLW without slag formation along the boiler path. There is a possibility of improving the thermotechnical characteristics of VUT. Composition VUT should be modified so that while maintaining viscosity μ ₀ = 0.45 Pa.s temperature T _m and T _m were approximately equal to each other.

The calculations showed that in order to achieve the task, the chemical composition of the ash, the ash content and the moisture content of the fuel should be regulated.

=11,85 МДж/кг, А^d=7%, w=50%. При этом Т_т=1051°С примерно равна температуре Т_ш=1057°С.The following composition of VUT was obtained:

= 11.85 MJ / kg, A ^d = 7%, w = 50%. In this case, T _t = 1051 ° C is approximately equal to the temperature T _w = 1057 ° C.

The calculation by the formula (1) showed that the condition V _d > V _cr is met.

The preparation of HFM includes gravity enrichment of coal crushed to minus 3 mm to ash content A ^d = 7.0%, grinding the coal to size with an average surface diameter of the solid phase of "-3 microns" and thickening the coal to a moisture content of 50%.

In this example, the ash content and chemical composition of the ash were controlled by gravitational enrichment of crushed coal, and humidity was controlled by changing the concentration parameters of crushed coal.

Example 3

The gas-oil boiler BKZ-120-100 is converted to VUT from Kuznetsk SS grade coal.

Coal has the following initial characteristics:

=35,59 МДж/кг,

=9%.

= 35.59 MJ / kg,

= 9%.

Chemical composition of ash:

SiO ₂ = 0.67, Al ₂ O ₃ = 0.21, Fe ₂ O ₃ = 0.04, CaO = 0.02, MgO = 0.01, K ₂ O = 0.04, Na ₂ O = 0.004 TiO ₂ = 0.009; P ₂ O ₅ = 0.002.

=16,70 МДж/кг, w=45% и вязкостью μ₀=0,5 Па·с.Calculations show that from coal with the initial ash content it is possible to obtain VUT with

= 16.70 MJ / kg, w = 45% and viscosity μ ₀ = 0.5 Pa · s.

The aerodynamic calculation of the boiler and the calculations by formula (1) show that the volume of the flue gases generated satisfies the condition for exceeding the critical velocities for ash particles.

Calculations by the formula (2) give the value of T _W = 1121 ° C.

The thermotechnical calculation of the boiler, performed according to the standard method, gives the value of T _t = 1194 ° C.

Since T _W <T _t , the combustion of HLW of the calculated composition without slagging along the boiler path is impossible.

=15,73 МДж/кг,

=14%, w=45%, SiO₂=0,85, Аl₂O₃=0,10, Fe₂O₃=0,02, СаO=0,01, MgO=0,004, K₂O=0,02, Na₂O=0,002, TiO₂=0,004, P₂O₅=0,001.The calculation showed that in order to obtain the composition of the HLT, which ensures combustion without slagging, 5% (of the working mass of coal) SiO ₂ should be introduced into the composition of the crushed solid phase of the fuel. This leads to an increase in the slagging temperature T _W to 1194 ° C and a simultaneous decrease in the temperature at the outlet of the furnace T _t to 1187 ° C, which ensures the combustion of HLW without slagging. This composition of the VUT has the following characteristics:

= 15.73 MJ / kg,

= 14%, w = 45%, SiO ₂ = 0.85, Al ₂ O ₃ = 0.10, Fe ₂ O ₃ = 0.02, CaO = 0.01, MgO = 0.004, K ₂ O = 0, 02, Na ₂ O = 0.002, TiO ₂ = 0.004, P ₂ O ₅ = 0.001.

With the specified characteristics of the VUT, the condition v _d > v _cr is observed.

The preparation of HF includes grinding the source coal to a particle size with an average surface diameter of the solid phase of “-3 μm”, introducing the additive and thickening the coal to a moisture content of 45%.

In this example, the ash content of the solid phase and chemical composition of ash regulation VUT conducted by introducing the additive SiO _2, which provide a decrease in temperature T _m and T _m, allows burning VUT without shlakaobrazovaniya of the gas duct of the boiler.

If the change of temperature T _m values to produce by increasing the amount of water, the decrease of calorific value VUT substantially more (58% to 9/74 MJ / kg). Fuel consumption in this case almost doubles (1.77).

It should be noted that when burning HLW, the problem of ash collection is very effectively solved using standard ash collectors. This is due to the fact that during the combustion of HLW, all of the fly ash of the fuel agglomerates into hollow xenospheres (agglomerates) larger than 30 microns. Such large agglomerates are easily captured by conventional cyclone separators with efficiency up to 98-99%. Electrofilters can also be used effectively for cleaning combustion products from ash agglomerates.

The proposed method of burning fuel oil has been successfully tested by burning fuel oil made from brown coal from the Shurab field in a gas-oil boiler DKVR-4/13.

The proposed method allows to burn water-coal fuel VUT in gas-oil boilers and expands the possibilities of using VUT in heat power plants.

Claims (2)

1. A method of preparing water-coal fuel for combustion in a gas-oil boiler, including gravity enrichment of coal, crushing coal, wet grinding of coal to a particle size with an average surface size of the dispersed phase of not more than 3 μm, characterized in that moisture, ash, chemical composition are determined by preliminary calculation. ash, ash slagging temperature and calorific value of water-carbon fuel based on the conditions for the formation of such an amount of combustion products in the boiler that ensures achievement in the furnace when the boiler rises, the rate of combustion products is higher than the critical rate at which ash particles precipitate, and the conditions that the temperature of the products of combustion of coal-water fuel at the outlet of the boiler furnace should not be higher than the ash slagging temperature, gravity enrichment of coal is carried out before grinding and regulate humidity, ash content, chemical composition of ash, ash slag temperature and calorific value of water-carbon fuel in accordance with preliminary calculations. 2. The method according to claim 1, characterized in that when the temperature of the combustion products at the outlet of the boiler furnace is increased, it is reduced by changing the chemical composition of the ash of coal-water fuel due to the introduction of mineral additives, which use refractory metal oxides, for example SiO ₂ .