FR2458753A1 - COMBINED DRYING-MILLING AND COAL COMBUSTION PROCESS FOR INCREASING HEAT RECOVERY - Google Patents

Abstract

THE PRESENT INVENTION RELATES TO A NEW COMBINED PROCESS FOR DRYING-CRUSHING AND COAL COMBUSTION. THIS PROCESS IS CHARACTERIZED IN THAT THE PART OF THE QUANTITY OF AIR THAT ESCAPES FROM THE CRUSHER 1 AND WHICH CONTAINS CHARCOAL DUST, AND WHICH IS NOT NECESSARY AS PRIMARY AIR, IS USED FOR HEATING SECONDARY AIR AND OR FOR COOLING THE FUEL. NON-POLLUTING AND ENERGY-SAVING PROCESS.

Description

The present invention relates to a process

  non-polluting and energy saving, combining the drying

  grinding and milling of coal with the burning of coal, reducing the amount of primary air, even in the case of coals with high humidity. The formation of the flame exerts an influence

  essential for the energy consumption of furnaces.

  ment. To have a low heat consumption, it is necessary to use a fast combustion with a favorable transmission of the heat by means of a flame

  short and hot. Together with other factors,

  some sizes appear important for this purpose the proportions of primary air and secondary air as well as

  the primary air temperature and the conditions of the impulse

  insufflation. The proportion of primary air must be

  as small as possible and the temperatures of the primary air

  Mayor and secondary air as high as possible. The insufflation rate and the swirl component

  of combustion in the oven must be able to be determined

  born freely in an optimal range.

  The following processes for the combustion of coal are known to date: 1. indirect combustion, 2. direct combustion,

  3. semi-direct combustion, with or without additional filters.

  In the case of indirect combustion, the

  drying and grinding of coal is exploited

  in a manner completely independent of

  so-called in the oven. In this process, one can optimize

  the determining factors of flame formation, inde-

  from the coal drying and grinding plant. It is however necessary to provide a filter

  separate unit for the purification of the air escaping from the

  grinding chamber and which contains dust, as well as an intermediate storage tank for dry crushed coal; Therefore, this process represents a danger with regard to the risks of explosion and fire of the dust of

  coal; on the other hand, the costs of investments,

  care and maintenance are high.

  In the case of direct combustion, it is not

  In the treatment furnace, all of the air that escapes from the grinding plant contains coal dust. The investments are significantly lower since, for example, a separate filter for purifying the air which escapes from the grinding plant and which contains dust may be dispensed with, and intermediate storage tank of dry milled coal. The danger of explosion and fire of coal dust is significantly reduced in significant proportions due to the absence of these intermediate devices and process phases associated with it. It is formed however,

  disadvantageously, high proportions of primary air

  mayor, which makes it impossible to obtain optimum conditions

  Inhalation instillation at the burner.

  In the case of semi-direct combustion, the air that escapes from the grinding plant and contains coal dust is pre-dusted in a cyclone. Part of this air is reintroduced as recirculation air in the grinding system and is used as additional air-carrier in the

  grinder, while the rest is blown into the joint oven

  with the coal dust that separated in the cyclone. In the case where the moisture content of the coal is high and where the heating of the mill is carried out at low temperature

  high, it results from drying an amount of exhaust air

  more important than that which corresponds to the amount of carrier air required. In cases of this kind, it is advisable to provide either a high quantity of primary air, or the installation of a supplementary filter. It

  disadvantages, just as in the combustion of

  or indirect. Thus a high amount of primary air prevents the optimization of pulse conditions

  insufflation in the oven burner, and that a filter

  additional investment and danger

  higher explosion and fire of coal dust

  good. It is therefore an object of the present invention to provide a process in which the proportion of primary air can be selected and kept low at will,

  irrespective of the moisture content of the coal and the heat

  mill, and in which the conditions of insufflation

  the burner nozzle can be adjusted inde-

  from the drying and grinding process without having to provide a separate filter for coal dust or an intermediate storage tank, and avoiding the risks and additional costs associated with it, as is the case in the indirect combustion plants, the method which is the subject of the present invention also allowing the recovery of heat from the escaping air

of the grinder.

  This object is achieved according to the present invention, in that secondary air is used for heating and / or for cooling the fuel, the part of the air that escapes from the grinding plant and that contains coal dust, which is not

  needed as primary air.

  According to a preferred embodiment of the invention

  beforehand, by means of a preliminary purification process, in particular in a cyclone, the part of the air which escapes from the mill and which is not necessary as primary air, and this dedusted air is used for the cooling of the fuel and / or the heating of the secondary air, so that the heat of the fuel is also recovered with a view to

  heating the air that escapes from the mill.

  According to yet another preferred embodiment

  In accordance with the invention, the hot air which escapes from the mill and which contains coal dust is blown into the hot front part of the cooling apparatus for the clinker, so that here also the heat

  is recovered and the remaining coal dust is

  flame, furthermore, in this hot zone, so that it is eliminated to a significant extent and that it can still

  be used to heat the secondary air.

  According to yet another preferred embodiment

  d of the invention, air that escapes from the mill is blown under the grid of the cooling apparatus for

  clinker after said air has been previously

  sere using a preliminary purification process. According to another preferred embodiment of the subject of the invention, the air which escapes from the mill is

  blown over the grill of the cooling device

  clinker, after having been previously dusted

  using a preliminary purification process.

  According to yet another preferred embodiment

  of the process which is the subject of the present invention,

  charcoal is used to produce hot air

  cooling apparatus for clinker or

of the oven head.

  According to yet another embodiment of the invention, it is used for the drying of coal,

  hot exhaust gases coming out of the oven.

  According to another particular embodiment of the invention, it is used, for the drying of coal,

  a combustion process of its own.

  The process according to the present invention

  comes particularly to the process of calcining the

  clinker of cement, lime or spongy clay, using

  a rotary kiln system followed by a planetary, tubular, bowl

fluidized bed.

  Said method also applies to the

  cessation of calcination of cement clinker, lime or spongy clay, when using a shaft furnace

  or a trolley furnace moving by pushing.

  The process which is the subject of this

  vention is also suitable in the case where a roll mill and trough mill or a ball mill is used

for drying and grinding.

  Finally, the process according to the present invention

  It is also appropriate in the case where a

  combustion using exclusively coal as well -

  mixed combustion using coal and

other fuels.

  The aforementioned possibilities of use of the method according to the present invention are only examples and are not to be considered in any way as limiting. This makes it possible to limit the portion of the quantity of primary air required for the burner of the oven to the amount

  necessary for optimum combustion, independently of

  the drying and grinding system and the moisture content of the coal, while introducing the remaining amount of air that escapes from the mill, in an energy-efficient and non-polluting manner, without

  to use a particular filtration system.

  The process according to the invention is energy efficient, in that the heat contained in the hot air escaping

  The grinder is reused for heating secondary air.

  On the other hand, the remaining coal dust from the air which escapes from the mill is brought to the secondary air, so that it is not necessary to separate it by filtration; in particular, this residue of coal dust may be burnt in the secondary air stream, according to a particular embodiment of the process which is the subject of the present invention. This represents a more direct and complete use of all the coal dust contained in the air that escapes from the mill, so that the process according to the invention is not only economical in energy and raw material. , but also operates in a non-polluting and less expensive way, since the remaining coal dust is removed and that, in this way, a

  Separate filtration facility is no longer needed.

  It should be added that we can reach

  safety against explosions and fires.

  dies due to coal dust, by carrying out the process which is the object of the present invention, by avoiding the use of an intermediate storage tank of coal dust and a filtration installation and thanks to

  the possibility of exploiting and controlling the

  drying and grinding without any heat loss

  significantly, even when the moisture content of coal is high, by implementing relatively low hot air temperatures; moreover, the problems posed by the high humidity levels of the coal are eliminated easily by largely using the residual heat of the furnace and /

  or the cooling apparatus for the clinker.

  In addition to the foregoing, the invention also includes other arrangements which will be apparent from

the following description.

  The invention will be better understood by means of

  additional description which follows, which refers to

  attached drawing in which - the single figure shows schematically an apparatus for implementing the method which is the subject of the

  invention, which apparatus contains, in particular

  a cement kiln and a cooling device

  with sliding grid for the clinker.

  It should be understood, however, that this drawing and the corresponding descriptive parts are

  given only as an illustration of the purpose of the in-

  which they do not in any way constitute a limitation

  tation. The coal, dried and ground in a coal mill 1, is separated in a high-power cyclone 2, after which it is introduced, via a closure member 3, into the primary air stream or into a

  partial air flow of the primary air stream 4.

  The quantity of air or gas necessary for drying and as a carrier air is drawn through the coal mill 1 and the high-power cyclone 2 using a blower 5. It is used as a means of transport and as drying means, upstream of the coal mill 1, either hot air from the cooling apparatus which passes through the air line of this apparatus, or hot air from the head of the furnace which passes through the air line 7 of the furnace head, that is to say the exhaust gases of the furnace which pass through the furnace exhaust pipe 8,

24581S3

  either hot gas from a combustion chamber 9,

  or combinations of air from the cooling device

  air from the furnace head, exhaust gas

  Oven and hot gas, using for the adjustment the cooling air valve 10, the valve It air from the oven, the valve 12 of the oven exhaust and the valve 13 of the chamber of combustion, as well as the cold air valve 30, the hot air containing dust

  having been purified beforehand in a cyclone 14. The air escaping

  For example, the grinder, which contains coal dust, previously dedusted in the high-power cyclone 2, is divided downstream of the blower 5 and can be directed both towards the primary air blower 15 and towards the inlet. of the mill, through the flap 19 disposed on the communication pipe 18, or even towards an air blower

  cold 16 of the cooling apparatus 17 for the clinker.

  The proportions of these different quantities can be optimized and regulated each time in a range from 0 to 100%, depending on the requirements of the grinding system, the

  moisture content of the coal and the formation of the flame.

  This is what serve the flap 19 of the connecting pipe, the intake flap 20 of the cooling air and the emergency flap 21, as well as the primary air flap 22

  and the flap 23 serving for the supply of cold air.

  These adjustment possibilities make it possible to reduce

  to maintain the proportion of primary air at will and to use the most different burner nozzles 24, as well as the most diverse combinations of combustion, by using, for example, complementary fuel 36, without being

  necessary to take into account the moisture content of the

  good and conditions prevailing in the drying installation

and grinding.

  Thus, a higher amount of air that escapes from the mill is blown into the cooling apparatus for the clinker, particularly in the case of a high moisture content of the coal. Insufflation takes place,

  for example, using a blower 16 of cooling air

  directly in one of the cooling chambers.

  31. Inflation, however, may also be

  distributed over several blowers 16 of cooling air

  or it can be transferred with the help of a

  flante 34 separate supply air cooling in one or more chambers 31 of cooling air, or directly in the part of the cooling apparatus for clinker 37 which contains hot air, via However, it is preferable to blow in the cooling air chamber 31 closest to the part of the cooling apparatus 37 for clinker which contains the hot air. In this way, the thermal heat of the air escaping from the mill can be fully utilized for reheating of the secondary air. In addition, the fraction of non-thermal heat still contained in the air escaping from the mill, is ignited in the form of the remainder of the coal dust during its passage through the hot layer of clinker, and

  is thus used. Said fraction of heat serves to heat

  iron more secondary air. The excess air that escapes

  the cooling apparatus is fed through the

  diary of the outlet pipe 32, the outlet dust collector 27 in which it is dusted. The exhaust air is driven to the open air depending on the pressure in the furnace head, using the air blower 28

  exhaust and regulating valve 29.

  In the process which is the subject of the present invention, and unlike the indirect process, all the heat of the escaping air, that is to say both thermal heat and heat contained in Residual carbon dust from the exhaust air is recovered

  In addition, because of the burning of the whole of the

  residual coal, it is no longer necessary to provide a carbon filter. This represents a significant saving and a significant increase in the safety of the operation. Similarly, no more coal dust escapes to the atmosphere, so that the process according to the invention is substantially less polluting than the methods known hitherto. It is no longer necessary to provide intermediate storage of the coal dust, so that the danger of fire or explosion due to coal dust is reduced in a significant proportion. As a result, the overall costs of investment,

  monitoring and exploitation, much smaller.

  Unlike direct or semi-direct processes, the amount of primary air may, in accordance with the present invention, be determined at will. As a result, flame optimization can be achieved and the amount of primary air can be kept at a much lower level. This results in fuel savings which, in the case of high humidity coal, can reach about 100 kg / calorie per kg of clinker (0.42 d / t

clinker).

  As is apparent from the above, the invention is not limited to those of its modes of implementation, implementation and application which have just been described more explicitly; it embraces, on the contrary, all the variants that may come to the mind of the technician in the field, without departing from the framework, or

  the scope of the present invention.

Claims (12)

  1. A non-pollutant and energy saving method of drying, grinding and burning coal by reducing the amount of primary air even when the coal has high levels of moisture, which process is characterized in that part of the amount of air that escapes from the mill (1) and which contains coal dust, and which is not needed as primary air, is used for secondary air heating and /or for the cooling of the fuel.   2. Method according to Claim 1, characterized   in that the part of the air that escapes from the grinder (1) pre-   laundered dust with the aid of a pre-treatment apparatus   limestone, in particular a cyclone (2), not used as primary air, is used for cooling   fuel and / or for heating secondary air.   3. A method according to any one of the   1 and 2, characterized in that the hot air which escapes from the mill (1) and which contains coal dust is blown into the hot part of the grid (25) of a cooling apparatus (17). ) for the clinker, so that not only the thermal heat of the air, but also the heat of combustion of the residual carbon dust of the air, is recovered for the heating of the secondary air. from the mill (1), which ignites in the hot part of the cooling apparatus (17) for the clinker.   4. Process according to any one of the   1 to 3, characterized in that the air escaping from the   grinder (1) and which has been previously dusted with   tion-preliminary, is blown under the grid (25).   5. Process according to any one of the   1 to 3, characterized in that the air escaping from the   crusher (1) and which has been previously demolished by purification   Preliminary draft is blown over 14 grid (25).   6. A method according to any one of the   1 to 5, characterized in that it is used for drying   coal, hot air from the heater   it chills (17) for the clinker or the oven head.   7. Process according to any one of the   1 to 6, characterized in that it is used for drying   coal, hot exhaust gases from the furnace. 8. Process according to at least one of   Claims 1 to 7, characterized in that one uses a   separate combustion for coal drying.   9. Use of the process according to any one of   Claims 1 to 8, characterized in that said method   is used for the calcination of clinker cement, lime or spongy clay, using a rotary kiln system followed by a cooling device   planetary, tubular, tub, or fluidized bed.   10. Use of the process according to any one   Claims 1 to 8, characterized in that said method   is used for the calcination of clinker cement, lime or spongy clay, using a shaft furnace or   with carriage moving by pushing.   11. A method according to any one of the   1 to 8, characterized in that one uses a -   roller mill and trough mill, or a ball mill for drying-grinding.   -12. Process according to any one of the   cations 1 to 8, characterized in that one uses a   combustion using only coal, or   mixed use of coal and other fuels.