US2159849A - Plant for pulverizing and burning coal - Google Patents

Description

May 23, 1939.

a. GRAEMIGER PLANT FOE PULVERIZING AND BURNING COAL Filed Jan. 6, 1956 EN AMIN v ESFQAEMIEEF? Patented May 23, 1939 UNITED STATES PATENT" OFFICE PLANT FOR PULVERIZING AND BURNING COAL Benjamin Graemiger, Zurich, Switzerland Application January 6, 1936, Serial No. 57,822 In Switzerland January 8, 1935 3 Claims.

The invention relates to a method for operating pneumatic pulverizers in which the grinding operation is effected by a stream 01' gaseous operating medium (as a rule air). The work pro-.

ducing stream is forms 9 by the-expansion of the I operating medium in one or more suitably shaped nozzles. The operating medium must becom pressed and in most cases a heating also takes place after the, compression whereby the energy, thatis to say the velocity .of the stream, which is set free as -a result of the expansion is increased, When a predetermined energy of ex-' pension is. to be converted in the pulverizer the work of compression becomes the smaller the I higher the temperature of the operating medium, ,whether a lower pressure is produced or the quantity of operating-medium selected-is smaller. Heating operating mediumalso promotes the drying of the material to be-ground which is generally damp, during the puverizing' operation and by the' drying the capacity of thematerial to grinding is also improved in most cases, The heating of, the compressed operating medium is consequently :2

advantageous for numerous reasons in most cases.

To the advantages of 'the pneumatic ,pulverizer, in connection with'which there istobe' particularly emphasized the omission of movable constructional parts in the pulverizer itself, there is opposed in many cases and even when the heating of the operating medium'is carried to ,a farreaching extent, a high'requirement of energy for the compression of'the gaseous operating medium as, compared with the requirement of energy by.

' pulverize'rs of a diflerent type.

The compression energy is taken up a motor which drives the compressor. inmost casesthis is an electric motor, occasionally also a steamturblue. t i

The invention has for its object to reducefthe cost for compressing the operating mediumand,

thusfor the pulverizing; The invention'resides therein that into the gaseous operatingmedium, of which at .least one part serv'es'for the operation of the pulverizer, there is' supplied, by compression and heating,,a larger amount of energy than is necessary for the operation of the pulverizer and that theexcess energy is utilized-in a power'engine which drives the compresson In this manner it becomesipossible to carry out the compression work-necessary for the operation: of

the pulveriz'er at least in part by heat supplied to the operatingv medium and thus wholly or partly to effect an economy in the consumption of mechanical or electrical energy. In most cases the price for heat and the price for mechanical or electrical energy are inf'such a relation that the expense involved for. the-pulverizing according to the method according to the invention is consld-.

erably less than according tov one 'of [the methods hitherto-usual. Frequently also the heat which has been introduced may again be utilised so that it is possible to effect a pulverizing which is practically costless;

The necessary excess of energy may be produced vinthat a. quantity of operating medium greater than that necessary for the operation of the pulverizer is compressed and heated and the. excess of operation medium is expanded in a power engine which drives the compressor. This method becomes particularly advantageous when the Such a plant becomes particularly simple .when l the whole of the combustion air is supplied by the cpmpressor, of which one part serves as the operating air for the pulverizer and thus as the .3

primary air, and the other part after expansion has taken place as the secondary air. A separate blower together with a' driving motor for the secondary air then becomes unnecessary.

compressing the operating medium serving for the operation'of the pulverlzer to a pressure which is higher than thathecessary-for operating .the pulverizer and after heating expanding it in a power engineserving to drive the compressor, at least approximately to the pressure necessary'for operating the pulverizer. In this connection it may occur that, the operating medium after expan'sion has taken place in the power engine is still too hot to be capable of being used for operatingthe pulverizerr In this case heat is withdrawn from the operating medium before it heat in any suitable manner. This may preferably be effected in that the withdrawn heat is supplied to theoperating-medium between the compressor and the power engine. i

In the/case. in which at'least apart of the :operating medium is separated beyond the pulverizer, from the line material produced, in a separator, this part may also be used for heating the operatingmedium between the compressor and the po'wer engine Naturally any otheruse of this .waste heat is possible, if desired also in There is then not only supplied The excess energy may also be obtained by enters the'pulveriz'er, whilst naturally endeavours v are always made to again use this-withdrawn heat still contained in the excess -of operating 1 mediumafter expansion can be made capable grinding plant.

There may also be used a quantity of operating medium which is larger than that necessary for the operation of the pulverizer and to compress this to a pressure higher than that necessary for operating the pulverizer. The part of the operating medium necessary for the operation of the pulverizer then expands in the power engine driv-. ing the compressor to the pressure necessary for the operation 'of the pulverizer, whilst the excess of operating medium expands in a power engine to a pressure lower than that necessary for operating the pulverizer The expanded excess operating medium can then again be used for heating the operating medium between the compressor and the power engine.

When the heat supplied to the system is not sufficient for obtaining the energy for compression 0. motor can support the power engine in which the operating medium expands. It is particularly advantageous to include in the flow of the operating medium'an additional compressor which is then in turn driven by a motor of any suitable type. Auxiliary energy may also be supplied to the system in that a compressed gaseous medium of any suitable typeis introduced into the operating medium supplied by the main compressor. This may be effected, for example, in that an auxiliary compressor driven in any suitable manner, operates in parallel with the main compressor, or a medium, in 'vapdur form, under. pressure is supplied. The supply of such an additional medium may be effected before or afterxheatingth'eoperating mediiun. Such an introduction of additional medium particularly arises during the period of starting such a plant.

.power engine 4 (in which the operating medium expands). 5 is the pneumatic pulverizer to which the operating medium is supplied through the pipe l0, whilst the material to be pulverized is supplied through the pipe I5 and the dust produced flows ofi with the operating medium (expanded in the pulverizer) through the pipe [4. 1 is the suction pipe of the main compressor 3. In the admission pipe 9 of the expansion power engine 4 is included the device for heating. the operating medium which in Fig. l, is constructed as a surface heat exchanger ll, 12, whereas the operating medium in the case of Fig.2 is heatedin. a combustion chamber 13 subjected to the pressure of the operating medium. In Fig. 2, there-is shown an auxiliary compressor 2, arranged in front of the main compressor, and 6 is the suction pipe of the auxiliary compressor 2. In Fig. 1 there is included in the pipe 8 also an additional heat exchange device [6, I1 through which the heat withdrawn from the expanded operating material is conducted into the compressed operating medium.

As regards the diagrams the following may also be mentioned in detail by way of explanation. Assuming that the temperature of the operating medium, which flows through the pulverizer', may not be as high as the temperature of the part which flows through the expansion power engine 4, there is effected in Fig. 1 a branching of the pipe [0 between the heat exchanger l6, l1 and the heating device ll, i2. It is also possible to branch the supply pipe to the pulverizer from an intermediate stage of the heat exchanger 1 I, I2 as is indicated in'Fig. 1 by the broken line We. The coupling between the motor and the group,'consisting of the compressor 3 and the power engine 4, may be effected directly or through the interposition of a transmission gear. The heating of the operating medium in the heat exchangers ll, l2 maybe effected, for example, by the waste heat of a steam generator.

In Fig. 2, the heating of the operating medium is effected by the combustion of any supply found in the combustion chamber i3 which is arranged between the pipes 8 and 9. 3| indicates the supply pipe for the fuel. In front of the combustion chamber a first portion of the operating air is passed through the pipe 38 and behind the combustion chamber there is branched a second .portion" for the pulverizer through the pipe 39.

The two pipes are combined into the pipe Ill. In the pipe 38 is included a regulating member 40 by which the temperature of the mixture in the pipe I0 can be influenced. The driving motor I is here not coupled mechanically to the group 34 but it drives the additional auxiliary compressor 2. Such a compressor could also be included in the pressure pipe 8, further an additional compressor could be arranged in parallel with the main compressor. By the pipe 4|, indicated in broken lines, is indicated an alternative by means of which an additional operating medium is supplied to the power engine 4. When for example 4 is a hot air turbine, then water vapour could be supplied through 4| for supporting the operation by providing for this purpose an auxiliary nozzle. Such an auxiliary device may also be provided adjacent an actual driving 'motor so as to provide supplementary means when starting or when the plant is subjected to an extremely high load. For the internal combustion in the chamber 3, there may be selected a solid, liquid, gaseous, or mixed fuel. The heating may also be so effected that a first stage takes place by indirect heating (Fig. 1) and a second stage by internal heating. The use of one part of the waste heat of the exhaust air of the power .engine 4 for heating the air in the pipe 8, may naturally also be carried out within the scope of the diagram in Fig. 2.

For completing the explanation as to the method of operation in Figs..1 and 2, there will be hereinafter set out numerically a first example. In a furnace plant with direct blowing in of coal dust produced in a pneumatic coal mill, the amount of coal dust produced and burnt is assumed to be 1 ton/hour. The energy to be applied between the expanslon nozzle and the dust air outfiowing from the mill is 24 kw. which corresponds with a coal capable of being ground moderately well. At a temperature in front of the nozzle of 250 C. and a pressure ratio of 1.26 there is obtained a quantity of operating air of 2580 kg./hour. The total quantity of air necessary for the combustion is 12900 kg./hour (10 normal cubic meters/kg. coal). The compressor 3 supplies this total quantity of air, having regard to the resistance in front of and behind the mill at a; pressure ratio of 1.30. Assuming 20 C. in

the suctionpipe I, and a compression 'efiiciency adiabatic expansion of 80% there is obtained an output of 115 kw. so that the driving motor is entirely unloaded. Without taking up external mechanical or electrical energy, the grinding and conveying of the coal dust and in additionthe degree of pressure for overcoming the resistances are effected in the air heater and in the burner, The heat which is taken up is completely utilized in the furnace .42 (having an outlet 43) both with the primary air and also with the secondary air. This (in the case of the diagram Fig. 2) has in the pipe 34 a temperature of 460 C. The primary airis cooled during the grinding operation only to such an extent as is necessitated by the drying and heating of the coal. For both, however, it is no longer possible to supply the corresponding heat consumption in the furnace. It is well known that the operation of coal-dust furnaces is promoted to a high degree by high temperatures of the; combustion air which is supplied. In the ease of a steam generator it is in general also very advantageous to mount in the system an air pre-heater as subsequent heating surface. Should the temperatures here assumed lead to undesirable conditions in the arrangement of the subsequent heating surfaces of the heat generator, then the upper stage of the heating can be carried out separately either by an additional indirect heating or by internal combustion.

Under usual conditions of operation'the compressor would bring 2580 kg./hour operating air to the pressure ratio 1.30 and then take up an output of 27 kw. measured at the terminals of the ,driving electric motor. desired to eflect an air preheating to the same extent, as occurs in this example, there would also be the output of a secondary air blowenamounting to about 12 kw. The total gain thus amounts 'to about 39 kw. In the present example there is assumed a single stage rotary compressor and a single stage and single-bladed turbine.

In many cases, however, there exists between heat and current price a ratio which is still more favorable for the method according to the invention. This particularly occurs when the heat consumption can be supplied wholly or partly (particularly the low temperature sta'ges) .by waste heat of any type; Particularly favorable is the case where the heat introduced into the system can be used in any way. This for example is the case when the air charged with fuel passing outthrough the pipe I4 is conducted into a furnace chamber. 7 I

The carrying out of the method leads in most cases to the use of a single stage hot air turbine with a single or multi-stage compressor. These engine'"--'groups can be constructed in a particularly advantageous manner in that the suitable speed of rotation for the turbine and the compressor are well tuned to one another. There is consequently obtained a minimum of weight and space requirement. This is particularly the case when being used on vehicles of any kind of importance. The regulation of these groups is very satisfactory. For influencing the operation there arise for example; The variation of the ad- If, however, it is mission temperature of the turbine, the variation -of the nozzle cross section at the pulverizer, the

variation of any auxiliary energy that may be supplied.

The method according to the invention is in no way bound to the type of engines which are used for compression and expansion. Also there is no limitation to the selection of any auxiliary motor that may be required and in the method and manner of the introduction of the additional energy into the'system. The construction of the device for heating the operating medium may have any imaginable forms. The pneumatic pulverizer may have any form of construction. The circuits and devices for the heat transmission may depart from the examples here shown. As regards the pressure and temperature between the total quantity of operating medium and the part flowing to the pulverizer there is no limitation. In particular it is to be emphasized that also behind the pulverizer there may obtain an appreciable pressure above atmospheric pressure, as -is for example the case in connection with fuel pulverizing 'in combination with a furnace operating under pressure. There is no'restriction as regards either the' material to be pulverized or the gaseous operating medium to be used.

What I wish to secure by United States Letters Patent is:

1. A pulverizing plant which comprises in combination a compressor compressing a gaseous operating medium, means for heating the compressed operating medium, a power engine in which a part'of the compressed and heated operating medium expands and which drives said compressor, and a pneumatic pulverizer in which the other part of the compressed and at least in part heated operating medium expands, and

means for dividing the heated gas into two parts and for conducting one part to the pulverizer and the other part to the engine.

2. A pulverizing plant which comprises in combination a compressor compressing a gaseous operating medium, means for heating the compressed operating medium, a power engine in which a part of the compressed and heated operating medium expands and which drives said compressor, a pneumatic pulverizer in which the other part of the compressed and at'least in part heated operating medium expands, means for dividing the heated gas into two parts and for conducting one part to the pulverizer and the other part to the engine and means for transferring heat contained in the part of the operating medium expanded in said power engine into the operating medium leaving said compressor.

3. A plant for pulverizing and burning coal which comprises in combination a compressor compressing air, means for heating the compressed air, a power engine in which a part of the compressed and heated air expands and which drives said compressor, a pneumatic coal pulverizer in which the other part 'of the compressed and fully or partly heated air expands, means for dividing the heated gas into two parts and for conducting one part to the pulverizer and the other part to the engine, a furnace,

means for blowing the air expanded in said' pulverizer as primary air together with the pulverized coal directly into said furnace, and means for blowing the air expanded in said power engine as secondary air into said furnace BENJAMIN GRAEMIGIR.

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