US2230799A - Combustion system - Google Patents

Description

Feb; 4, 1941. I v c, HOBBS 2,230,799

' COMBUSTION SYSTEM Original Filed May 14, 1936 76 Stack Pressure Cold Air to PuIverizers Temperiny) Hot Air to Burners ai Gas Inlet,

Pulverizers Burmfrs 7-0/1 saw/5,

729 ,4 Bap m INVENTOR. James C Hobbs Pull/erizers Patented Feb. 4, 1941 cum-1o sr-A'rss PATENT; oFFlce Application may 14,1936, Serial No. 79,694

Renewed June 14, 1940 10 Claims.

19 verizer also carries the pulverized fuel in suspension to the furnaceburners and acts in part to support the combustion of the fuel.

With such pulverizing and burning installations, and particularly when they are used in con 15 junction with a steam'generator, it is desirable to use preheated air for the suspension of the pulverized fuel in its discharge from the pulverizer to the furnace and also for the additional air re- I quired to complete the combustion of the fuel.

20 The temperature requirements of the twdstreams of air differ, the ratio of one air volume to the other also differs, and the total quantities vary with boiler load, yet for reason of economy itis desirable to raise their temperature by the same 25 source of heat, the waste stack gases.

In addition, the air which is passed through the pulverizer is subjected to greater flow resistance and the prwsure at which it is supplied must be higher than 'the secondary air which is passed 80 directly from the source of heat to the furnace.

It is an object of my invention to provide such an advantageous arrangement of air heating surface and fans, with respect to the waste gases from the boiler furnace, and the pulverizing and 35 burning equipment, that the two streams of air can be effectively supplied at the required pressures, temperatures, total volume, and volume ratios; without consumption of excessive power to drive the fans.

n Attempts to pulverize coal of a high moisture content have .shown serious reductions in mill output. Such coal has further interfered with effective operation of the mill, or pulverizer, and

increased its power requirements to such an ex- 45 tent that it is necessary to provide some method or apparatus for drying the coal either before or during its passage through the pulverizer.

' When air is forced through the pulverizer to assist pulverization and to carry away the pul- 50 verized coal, it can also be used to dry'this coal if its temperature is high enough, but this temperature must not be so high as to cause excessive distillationof the volatiles,

, The quantity of this primary air must'be ad- 55 justed to the requirements of pulverizing and of carrying the pulverized coal in suspension to the burners, but the temperature of such quantity must be adjusted to the requirements of drying coal of variable moisture content, while the quantity of secondary air must be so adjusted that 5 the sum of the quantities of primary and secondary air is adjusted to the rate of fuel feed to be no more than sufilcient to completely burn it, and the temperature of the secondary air must be as high as practicable. Thus, the total air quantity must vary with the fuel burned which in this system' is equal to that pulverized, but the ratio of primary to secondary air must vary with rate of pulverization, while the temperature of the primary air is adjusted to coal moisture and that of the secondary is kept as high as practicable.

It is not only preferable that the primary and secondary air be supplied to the pulverizer within the above mentioned volume and temperature limits, but that the primary air normally be'supplied at a pressure higher than the pressure of the secondary air because of the fact that the former acts as carrier air in classifying and transporting the pulverized fuel through the pulverizer to a burner and is subject to flow restrictions which increase the pressure drop. It is an object of this invention to provide a system which will solve these problems without provision of separate air heaters at-separate positions in the path of the flue gases leaving the boiler furnace and without excessive power consumption by the fans.

A further object of the invention is to provide a combined steam boiler and pulverized fuel fired furnace system in which the supply of primary air is automatically controlled, preferably in response to variations in the pressure of the steam in the boiler. In conjunction with this'invention the primary air is supplied by a plurality of fans, any one of which may be selectively made opera- 40 tive and inoperative without an accompanying multiple operation of air-flow controllers.

Other objects of the invention will appear as the accompanying description proceeds.

The invention will be described with reference to the accompanyingdrawing which shows diagrammatically a system embodying the invention.

The illustrative system includes a furnace l3 fired'by pulverized fuel burners I2. When the furnace is apart of a steam generator, walls of the furnace may include wall tubes I i connected into the boiler circulation through headers such as the header It. In such an installation, the furnace gases pass across steam generating tubes .and then to the inlet l8 of an air heater 2t. Corn 553 duits may be appropriately arranged for so direct- I lets-of this fan are connected to the furnace gas discharge outlet of the air heater by the parts 26 and 28 of an appropriate breeching,

In such a system as that disclosed, primary air passes through fuel pulverizers to the burners, acting as carrier air to cause the pulverized fuel of proper fineness to move to the burners, and a larger quantity of'secondary air passes into the ignition zone of the. burners, independently.- When both the primary air and the secondary air are to be heated in independent parts of the same air heater, the latter is divide by such a partition as that indicated at 30. As s own, all that part, 32, of the air heater to the left of this partition is employed for heating the secondary air, the remaining part 34 being used for heating primary air. In the latter part of the air heater a plurality of furnace gas passages lead from the inlet I8 to the breeching28 and the heating of the primary air may be regulated by a controller 36 positioned at the furnace gas outlet of the air heater part 34.

The part of the air heater which acts upon the secondary air is supplied with air by a forced blast fan 38 and the secondary air is discharged from the air heater part 32 to a duct 40 leading to an air box42 which encloses the burners I2.

When the primary air forced draft fans 46 and 48 have their inlets 5| and 52 connected to the discharge side of the fan 38, the fans 46 and 48 act as boosters to cause the primary air to be delivered to the pulverlzers at a. pressure higher than that of the secondary air delivered to the burners. An arrangement of elements whereby such operation can be effected includes the duct 50leading from' the fan 38 and communicating with the cold air inlet (inletto the heater) 54 at one end and with the primary fan branches 56 and 58 at its other end. The

" controller 60 in the branchi58 will permit the fan 46 to be repaired or replaced without interfering with the operation of the fan 48, and the controller 62 will regulate the air delivered to theprimary air system by the fan 38.

The primary air fans 46 and 48 may be, when desired, independently connected on their inlet sides to the atmosphere through the branches 10 and I2, normally closed by the controllers I4 and I6. In the event that the fan 48 is to be temporarily taken out of service, the primary air fan 46 may be effectively continued in operation by operating the controller 80 to close that part of the conduit 50 between thev branches 58 and 56.

By the provision of air inlets I0 and 12, fan 46 or 48 can draw air from the atmosphere, allowing the entire discharge capacity of fan 38 to be directed throughthe section 82 of the heater and used as secondary air.

The air inlet side of the primary air section of the air heater communicates with a. memfold 821 having the branches .84 and 86 communicatlng with the discharge sides of the fans 46 and 48. These branches are preferably provided with automatically operating check damp-' ers 90and 82 which combine with the pressure operated controller I20 to facilitate the operation of the system. controller-is-preferably responsiveto steam pressure variations, and for that purpose it may be actuated by a-diaphragm' tothe operator I2I connectedby the tube I28 fer from one fan to another without removal.

drum 200 of the boiler. With this arrangement automatic regulation is attained, whether one or both of the primary air fans are in service. The control mechanism is simplified by making one controller take care of two fans and a plurality of pulverizers. Furthermore, it is a great convenience for the operators tobeable to transv I bothering with additional air-flow controllers.

' In order that the primary air delivered to the pulverizers I00, I02 and I04, may be tempered according to the moisture content of the fuels, and other conditions, the pulverizers are directly connected with the manifold 82 by a cold air duct I06, its manifold I08, and the branches H0, H2, and H4. In practice, all of this tempering or regulation may be done by the operation of the controllers I09, III, and H3, because by opening these, the higher pressure air in the cold air in the cold air manifold I08 causes enough tempering to obtain the desired pulverizer, or mill, temperatures. The pressure of the air in the manifold is greater than the pressure of the air supplied through the duct I22 because of the by-passing of the primary air heater.

The duct I22 leads from the primary air side of the air heater part 34 to a manifold I24. The latter communicates directly with the pulverizers through the branches I26, I28 and I30 which supply heated primary air direct to the pulverizers. The previously mentioned tempering air branches IIO-II4 preferably communicate with the branches I26-I30 at the sides of the latter as shown in the drawing, and dampers I25, I21 and I28 in the branches I26-I30 may be installed to provide for the independent control of the pulverizers and allow one pulverizer to be repaired while the others are operating.

Each of the burners I2 may be independently connected to a single pulverizer, and for the purposes of illustration, the conduit I50 is shown connecting one of the burners to the pulverizer I00. Similar conduits I52 and I54 connect the other pulverizers separately to other burners.

Referring again to the air heater, it will be understoodsthat the furnace gases originating in the furnace I0 pass into the inlet I8 at one side of the air heater and that solids carried in suspension by the furnace gases may be accumulated in the dust hoppers I60 for periodic The temperature of the .gases entering the inlet I8 will vary according to furnace operating conditions, such as rating, percentage of excess air, etc., and the variation in the heat transfer in the air heater must be compensated for in orderto provide the proper primary air temperature required by the moisture content of the fuel being pulverized.

In the operation of the illustrative apparatus, the primary air'may be delivered to the pulverizers at a pressure higher than the pressure of the secondary air and the temperature of the primary air may be regulated independently of the temperature of the secondary air. Thus, the temperature of the primary air may be kept sufliciently high to have adequate drying effect upon high moisture content fuels supplied to the pulverizers and at the same time the temperature of the primary air may be kept below a point at which it would cause excessive release of the tively .andeconomically than they would when both secondary air' andprimary airare intermingled and heated in the .same air heater and the primary air fans located beyond the air discharge side of the air heater. The life of the primary air fans under such circumstances isincreased and economy of original installation, as well as economy of maintenance are promoted, Furthermore, with the system shown, the operation of the system can be continuous even when one of the primary air fans must be temporarily taken out of service for repair or replacement.

What is claimed is: 1. In a pulverized fuel system comprisin a furnace, a burner, a pulverizer supplying the burner with fuel, an air heater divided into sections in which secondary air is heated separately from primary air, means for causing secondary air to flow through one of said sections to'the burner at a predetermined pressure, means in cluding a primary airline for causingprimary air to flow at a higher pressure from the first means through another of said sections to the pulverizer and thence to the burner, and a bypass for unheated air leading from the primary air inlet of the heater and joining the primary air line on the inlet side of the pulverizer.

. 2. In a pulverized fuel firing'system for steam boiler furnaces, fuel burning means through which pulverized fuel is projected into the furnace, an'air heater divided into sections in which primary air and secondary air are separately heated, means includinga forced draft fan causing secondary airto pass through one of said 1 sections to the fuel burning means, pulverizers supplying fuel to the fuel burning means, a bypass through which tempering air is supplied as a part of the primary air passing through the pulverizers in response to variations in the steam air section to the ignition zone of the burner pressure of the boiler.

3. Apulverized fuel combustion system, a furnace fired by pulverized fuel burner means, a pulverizer connected to the burner means so-as to supply pulverized fuel and primary air thereto. an air heater contacted by the furnace ases and having a secondary air heating section separated from a. primary air heating section, means direotly connecting the air outlet of the secondary means, means directly connecting thee-h outlet of the primary air heating section to the pulverizer, a forced draft fan supplying air to the secondary air heating section and causing it tov move under pressure to the ignition zone, a pin-- rality of forced draft fans for the primary air having their inlets connected with the discharge side of the forced draft fan for the secondary air, 65

duct means connecting the 1 discharge sides of the primary airv fans to the air inlet of the primary air heater section, a conduit leading directly from said duct means to the heated primary air connection to the pulverizer, means whereby the temperature of, the primary air delivered to the pulverizer may be controlled by varying the vol-' ume of'heated primary air passing to the pulverizerv or the volume of unheated primary'air passing to the connectionbetween the primary air section and the 'pulverizen-clamper means acting upon furnace gases independently heating the primary air section of-the heater tocontrol the temperature of the primary air, means whereby either or both of the primary, fans may have their inlet sidesconnected directly to the atmos-- phere while the connection with the cold air outlet of the secondary air forced draft fan is closed, and means wherebythe-operation of thesystem will be continued when either one of the primary air fans is removed forthe purpose of repair or replacement.

. 4, In a pulverized fuel firing system for a steam boiler furnace, fuel burner means, means for supplying secondary air to the burner means, a

primary air heater, pulverlzers, means for connecting the heater to the pulverizers for the supply of heated primary air thereto, a by-passconnected to the pulverizers for the delivery of unheated primary air thereto,'said by-pass communicating with the inlet of the heater and said connecting means, a plurality of primary air fans,-

separate check dampers for the primary air fans automatically closing the outlet of any one of said fans which may be temporarily-rendered inoperative, and means responsive to variations in steam pressure of the boiler for controlling the flow of primary air through the heater and through the by-pass.

5. In a pulverized fuel combustion system, a

furnace fired. by a pulverized fuel burner, a -pulverizer, means for connecting the discharge side of the pulverizer to the burner, a primary air the heater whereby primary air is delivered to thepulverizer, means including a forced draft fan for causing a movement-of heated primaryair to said connection to the pulverizer, a bypass connection which permits a movement of heater, a connection between the pulverizer and I unheated primary air to said connection, a forced draft fan causing secondary air to move to the ignition zone of theburner, and means 'connecting the inlet side of the primary air fan to the discharge side of the secondary air fan.

6. In a combustion system, a furnace, a fuel pulverizer, a fuel burner means receiving pulverized fuel and primary air from the pulverizer, a main supply of air under super-atmospheric passing a part of the main air supply and increasing its pressure as it is conducted as pri.'-.

' pressure provided by a main fan, means for bymary air to the pulverizer, means for dividing the by-passed primary airinto parallel streams, means for heating the air in one of the streams so that two streams of primary air at widely dif-r ferent temperatures pass toward the pulverizer,

means providing for the uniting of the primary air streams in regulated volumes before the pulverizer is reached, and means providing for. a supply of secondary air tothe burner means from said main air supply, I

7. In a combustion system, a furnace, a plurality of inde furnace, a pl ality of fuelpulverized through. each of which pulverized fuel ,and primary air is-supplied to a burner, a single blower through which passes the primary air for the pulverizers and thesecondary'airfor the burners, connections leading from the dischargeside of the blower tothe secondary airinlts 1 of all of the burners, other connections leading from the disl charge side'of the blower to the-primary air inlets of all of the pulverizers, said other connections including an additional blower, means for heating part of the primary air, means included in said other connections" for causing the rendently operable burners for the verizers.-

maining part of the primary air to by-pass the heating means, means whereby the said primary air parts are combined before entering the pul- 8. A pulverized 'fuel firing system comprising, in combination, a furnace, acpulverizer, a burner, 'a'secondacry air heater, a primary air heater, an

auxiliary cold air forced draft fan delivering primary air to the primaryheater and thence to the pulverizer so that itentrains pulverized fuel and carries it to the burner, and a main cold air forced draft fan deliveringv secondary air to the auxiliary fan and the secondary air heater in parallel, the secondary air being directed from the secondary heater-to the furnace.

9. In a combustion system, a furnace, a fuel burner, an air heater divided into first and second -air heating sections adapted to be heated by gases from the' furnace, means whereby said air heating sections are arranged for parallel gas'flow therethrough, means forming a, furnace gas inlet I and a furnace gas outlet common to said sections,

means including a forced draft fan causing air to pass through the first of said sections to the burner, means including a fan causing air to pass from the second 01' said sections to the fur-' air heating sections are arranged for parallel gas flow therethrqugh, means forming a furnace gas inlet and a furnace gas outlet common to said sections, independent means causing air to pass through said sections to the furnace, and means for controlling the heating gas flow over the first air heater section to regulate the temperature of the air therefrom.

JAMES C. HOBBS.

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