US1955255A

US1955255A - Air heater for pulverizers

Info

Publication number: US1955255A
Application number: US331056A
Authority: US
Inventors: John H Sengstaken
Original assignee: Foster Wheeler Inc
Current assignee: Foster Wheeler Inc
Priority date: 1929-01-08
Filing date: 1929-01-08
Publication date: 1934-04-17
Anticipated expiration: 1951-04-17

Description

April `17, 1934.` J, H. sENGs'rAKl-:N 1,955,255

A1B HEATER FOR Pummuzrms` Filed Jan. 8, 1929 Bw JMJ AroRNEY Patented Apr. 17, 1934 AIB HEATER FOB PULVEBJZEBS mm n. sengstaken. Brooklyn, N. Y.,

assignorto.V

s Foster Wheeler Corporation, New YorlnN. Y.,

a corporation of New York `Application January 8, 1929, Serial 12 Claims. (Cl. 11W-'104) The present invention` relates to steam gem, erator units in which powdered fuel is burned, generally in suspension, and in-which pulverizer units reduce the fuel to be burned to a neness y permitting burning in suspension. `In modern steam generators of this type it is customary to preheat all, or a maior portion,of the air required for combustion inan air heater located in the outlet iiue for the heating gases from the generator first and the air heater receives the gases after they have been partially cooled by their passage through the economizer. This arrangement has generally been considered to give the highest over-all efficiency inasmuch as both the air for combustion'and feed water are heated to the desired temperatures with a minimum amount of draft loss.

Difficulty has been experienced in pulverizing coal having a moisture content of, for example, over 15%. The moisture vcontent of such coal is often increased to 25% when exposed to snow and rain. Coal having a high moisture content has a tendency to pack in the pulverizer feed line and paddle chambers and materially increases the power requirements of the pulverizer. It is necessary yin such cases to provide some method of`or apparatus for drying the coal either before or during its passage through the pulverizer.

One system heretofore proposed involved the heating of the air for drying the coal by passing it through one or more air cooled furnace walls.

This system is impractical as the maximum temperature of the air attainable is about 250 F. which temperature with the amount of air available is not sufilcient to dry coal having a moisture content sufficiently high to present pulverizationv difficulties. It has also been proposed that a portionof the air heated for combustion purposes be diverted to the pulverizer. Additional air .heating surface is then required and the high air' temperature necessary in the pulverizer results in a material increase in cost of the air heater and ducts and the corresponding high temperature of the air for combustion increases the temperature in the furnace kchamber with a resulting increase in slagging troubles when coal of low ash fusingtemperature is used. Pro,- visions for protecting the furnace walls and'eliminating slagging are necessary with a corresponding increasein cost.

The object of my present invention is to provide an improved construction and'arrangement of the air heater, steam generator and pulverizer unit which is characterized by effective drying of the coal, reduction in power requirements of the pulverizer, and no increase in cost of furnace chamber construction.4 A further object the products of combustion.V `The air heater is normally positioned in the outlet flue in series with and after an economi'zer.` With this arrangement the'economizer receives of my invention is to provide aneasyand effective control ofthe 'amount delivered to the pulverizer unit.v

The various -features of novelty of'air heated `virliich"chai:-r acterize my inventionme pointed voutwith par- 'v ticularity in the claims annexed to and-forminga part of this specification.` fFor a'betterzuhder-f standing of the invention, however.- andthe ad`v vantagesl possessed by lit to the accompanying drawing and` descriptive:

preferred embodiments of the invention;

0f the drawing: f Y Fig. 1 is a diagrammatic viewof'one embodiment of the invention as assembled; andv ment.

I have diagrammatically illustrated a power plant unit comprising a'V steam generator A.' having a furnace chamber A' in'which powdered coal is adapted to be burned in suspension. The products of' combustion or heating gases pass upwardly into contact with a plurality of banks of water tubes A2 extending betweenV spaced drums A3 and out oi the generator through a passage gases are withdrawn from. the furnace by an induced 'draftfan A,`which delivers the gases to a stack connection A".

'I'he coal to be burned is comminuted in a pulverizer unit B located at one end of the generator and comprising a pluralityrof chambers in series in which the coal is reduced to the desired size by successive impacts with paddles B mounted 'in the chambers and rotated by an electric motor or steam turbine B8. The supply of unpulverized coal is continuously delivered through a chute to a hopper B2, from which it passes through a feed pipe B3 connected to the inlet end of the pulverizer.' Afan B4 -is positioned on the paddle shaft at the discharge end of the pulverizer for inducing a current of air through the pulverizer upon which the fuel in the course of treatment is borne successively from one paddle chamber to the next and when pulverized to the desired degree of fine-l ness is mixed with additional air for combustion entering the pulverizer through a. conduit B5 open to atmosphere. The air upon which the pulverized fuel is borne'is known as carrier air. The

combustible mixture is passed to one or more powdered coal burners ,B6 through a pipe B" connected to the fan discharge.

In carrying out my invention I provide an air heater C in the gas outlet iiue A'i adjacent the outlet passage A4. Air is delivered to the heater through a damper controlled conduit C' at room temperature from a forced draft fan C2. The air heater is so proportioned that only a relatively small quantity of air is subjected to the'furnace' reference should be had matter in which Ihave illustrated and described V'ns Fig. 2 is a similar view of a modified arrangea I In the drawing and particularly inv Fig.` 1` Y A* to a heating gas outlet flue A5. YThe coal and an auxiliary lbs. per 1b. of coal. This amount gases in the high temperature end of the conduit A5. The heater is much smaller in size than those ordinarily used for preheating all or a major portion of the air for combustion delivered to furnace chambers and the air exit temperature from the heater C is proportionally higher, normally ranging from 450 to 550 F. The heated air passes out through a conduit C3 connected to the pulverizer unit. The supply of air to the heater can be regulated either by controlling the speed of the fan C2 or changing the position of the conduit damper or both.

At the pulverizer end, the heated air conduit Ca is divided into branch conduits C5 and C6, each of which is controlled by a damper positioned therein. The conduit C5 is shown as connected to the inlet end of the pulverizer and the conduit C5 tothe discharge end of the pulverizer. The heated air from the conduit C5 comes into intimate contactwith the coal entering the pad- -dle chambers and thoroughly dries it.v This air is also used as the carrier air and carries the finely divided coal through the paddle chambers. As shown the conduit C5 is connected to the conduit B5 adjacent the connection of the latter to the fan chamber. A third conduit branch C'I connects the conduit C3 with the coal feed pipe B3 at a point vabove the connection of the latter with the pulverizer. The flow of air through the main conduit and each of the branch conduits being controllable by adjustment of the corresponding dampers, a close regulation of the amounts of air supplied to the different points in the pulverizer unit is possible.

An essential feature of the present invention is the delivery of a sufficient quantity of air at high temperature to the inlet or feed end of the pulverizer. This air contacts with the coal before and during its passage through the pulverizer. When this is suflicient to dry the coal, the branch conduits C5 and C'I remain closed. In practice the amount of air heated and supplied to the inlet end of the pulverizer varies from 1 to 11/2 of air is not sumcient for eiiicient combustion of the powdered supply of atmospheric air is drawn into the pulverizer through the conduit B5 by the fan. This air for combustion is not preheated but is at room temperature. yIf additional air is necessary, it is delivered by the fan C2` through the conduit C to the furnace chamber at room temperature. The amount of heated air delivered to the furnace chamber with the coal is relatively small in proportion to the air for combustion at room temperature and no measurable incerase in furnace temperature results. The furnace chamber construction need therefore be no more expensive than in furnaces not utilizing preheated air.

The overall efiiciency of the generator unit may be improved by the installation of heat absorbing surface, such as a standard economizer D in the, gas flue A5 below the air heater C. The usual pipe connections to the economizer and from the economizer to the circulating system of the generator are provided. While the temperature of the heating gases when they reach the economizer is less than in 'installations where the economizer is placed before the air heater, the exit temperature of the feed water is quite high and the use of such an economizer highly desirable.

In some cases it is advantageous to partially dry the coal while in the feed pipe B3 to improve the operation of the pulverizer feed mechanism. The damper in the conduit Crl is therefore opened to permit a small portion of the preheated air to pass to the feed line. This air is almost negligible in amount, but produces a marked improvement in operation of the feed mechanism.

Where the coal moisture content is relatively low and it is desired to preheat a portion of the auxiliary air for combustion, the conduit C7 is closed and the supply of air to the heater increased. The preheated air, at a slightly lower temperature than heretofore described, is proportioned between the conduits C5 and C5. The preheated air from the conduit Cs mixes with the air in the conduit B5 and passes with the dried coal to the fuel burners.

In Fig. 2 I have illustrated a modified construction in which the air heater is divided into two sections E and E having a common inlet connection from the fan C2 and separate discharge connections. This arrangement provides two sources of hot air at different temperatures and is particularly useful in pulverizer installations where the air passing through the pulverizer with the coal is desirably at a higher temperature than the air supplied to the discharge end. In thisrarrangement a conduit E2 connects the high temperature section E of the heater with the feed end of the pulverizer. A small branch conduit E3 connects the conduit E2 and the coal feed pipe B3. A conduit E4 connects the low temperature heater section E with the discharge end of the pulverizer through the auxiliary air conduit B5. The aggregate air heater surface in the arrangement shown in Fig. 2 is little, if any, greater than that of Fig. 1 and provides an eifective distribution of the heated aimyhen supplied to the three points indicated.

While in accordancewith the provisions of the statutes.: have illustrated and described the best forms of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus embodying my invention Without departing from the spirit of my invention as set forth in the appended claims and that in some cases certain features of my invention may be used to advantage without a corresponding use o.t other features.

Having now described my invention what I clalm as new and desire to secure by Letters Paten is:

1. 'I'he combination with a steam generator having a furnace chamber in which powdered fuel is burned in suspension, of a pulverizer uuit having means for pulverizing and delivering the fuel to be burned to said furnace chamber, and a sectional air heaterexposed to the heating gases from said furnace chamber, the sections of said heater being exposed to heating gases at different temperatures and heating air to differ-- ent temperatures, and separate discharge conduits for the different sections, said conduits beu ing connected to different points in said pulverizer unit.

2. The method of conditioning and feeding fuel containing excess moisture to a furnace which comprises feeding the fuel to a pulverizer, n

3. The method of conditioning and feeding fuel containing excess moisture to a furnace which comprises feeding the fuel to a pulverizer, supplying a small amount of highly preheated air to said fuel while it is being fed to the pulverizer, causing a relatively small current of earrier air at a temperature of over 300 F. to pass through said pulverizer, supplying a relatively large amount of air for combustion at a lower temperature than said carrier air to the outlet end of said pulverizer, and feeding the fuel by flotation on the combined air currents to the furnace, all of said air being substantially free from admixture with products of combustion.

4. The method of conditioning and feeding fuel containing excess moisture to a furnace which comprises feeding the fuel to a pulverizer, causing a relatively small amount of carrier air at a temperature of over 300 F. to pass through said pulverizer, supplying a mixture consisting of a relatively small amount of preheated and a relatively large amount of unpreheated air for combustion to the outlet end of said pulverizer, said mixture being considerably larger in amount and at a lower temperature than said carrier air, and feeding the fuel by flotation on the combined air currents to the furnace, all of said air being substantially free from admixture with products of combustion.

5'. The method of conditioning and preparing fuel containing excess moisture for burning in a furnace which comprises feeding the fuel to a pulverizer, supplying a definite amount of a gaseous heating medium to the inlet endof the pulverizer at a temperature above the melting point of the fuel, comminuting the fuel in the pulverizer, supplying a larger amount of a gaseous medium at a low temperature to the pulverizer at a point adjacent its discharge end to reduce the temperature at that point below the `melting point of the fuel, and feeding the comminuted fuel by flotation on said gases to the furnace.

The method of conditioning and preparing fuel containing excess moisture for burning in a furnace which comprises feeding the fuel to a pulverizer, supplying a dennite amount of a gaseous heating medium to the inlet end of the pulverizer at a temperature above the melting point of the fuel, comminuting the fuel in the pulverizer, supplying a larger amount of a gaseous medium at a low temperature to the pulverizer at a point adjacent its discharge end to reduce the temperature at that point below the melting point of the fuel, and feeding the comminuted fuel by notation on said gases to the furnace.

'1. The method of conditioning and preparing fuel containing excess moisture for burning in a furnace which comprises feeding the fuel to a pulverizer, supplying a definite amount of a gaseous heating medium to the inlet end of the pulverizer at a temperature above the melting point of the fuel, comminuting the fuel in the pulverzer, supplying a larger amount of a gaseous medium at a low temperature to the pulverizer at a point adjacent its discharge end to reduce the temperature at that point below the melting point of the fuel, feeding the comminuted fuel by flotation on said gases to the furnace, and regulating the temperature of the second mentioned gas in accordancewith the excess moisture contained in the fuel.

8. The method of conditioning and preparing fuel containing excess moisture for burning in a furnace which comprises feeding the fuel to a pulverizer, supplying a definite amount of carrier air to the inlet end of the pulverizer at a temperature above the melting point of the fuel, comminuting the fuel in the pulverizer, supplying a larger amount of air at alower temperature to the pulverizer at a point adjacent its discharge end to reduce the temperature at that point below the melting point of the fuel, and feeding the comminuted fuel by flotation on said air to the furnace.

9. The method of conditioning and preparing fuel containing excess moisture for burning in a furnace which comprises feeding the fuel to a pulverizer, supplying a definite amount of carrier air to the inlet end of the pulverizer at a temperature above the melting point of the fuel, comminuting the fuel in the pulverizer, supplying a larger amount of air at a lower` temperature to the pulverizer at a point adjacent its discharge end to reduce the temperature at that point below the melting point of the fuel, feeding the comminuted fuel by flotation on said air to the furnace, and regulating the temperature of the last mentioned air supply in accordance with the amount of excess moisture present.

l0. Apparatus for conditioning and feeding fuel containing excess moisture to a furnace which comprises a fuel pulverizer unit having a fuel inlet and a fuel outlet,-means for passing a relatively small amount of carrier air at a relatively high temperature through said pulverizer, means for supplying a lrelatively large amount of low temperature air for combustion directly to the outlet end of said pulverizer, .a furnace having provisions for burning pulverizedfuel in suspension, and means for conveying the pulverized fuel to said furnace together with the air supplied to said pulverizer unit..

11. In Vapparatus for conditioning and feeding fuel containing moisture to a furnace, the combination with a fuel puiverizer unit having a fuel inlet and a fuel outlet spaced apart from said inlet, means for progressively advancing fuel along a path of travel from said inlet to said outlet and subjecting the fuel to repeated pulverizer actions as it moves along said path and two air inlets opening to said pulverizer at separated points along said path one of which is less remote than the other from said fuel inlet, and

means for supplying preheated air at a relatively high temperature to the said `air inlet less remote from said fuel inlet and for supplying preheated air at a temperature lower than the first mentioned temperature to the other air inlet.

12. In apparatus for conditioning and feeding fuel containing moisture to a furnace, the combination of -a fuel pulverizer unit having al fuel inlet and a fuel outlet spaced apart from said inlet, means for progressively advancing fuel along a path of travel from said inlet to said outlet and subjecting the fuel to repeated pulver- ,izer actions as it moves along said path, two air supply connections opening to said pulverizer at separated points along said path one of which is less remote than the other from said fuel inlet and means for supplying preheated air at a relatively high temperature to the said air inlet less remote from saidv fuel inlet and for supplying preheated air at a temperature lower than the first mentioned temperature to the other air inlet said means including regulable means for admixlng air not preheated with preheated air passing to the last mentioned air in let.

JOHN H. sENGsTAKEN..