US2951457A

US2951457A - Ejector stack

Info

Publication number: US2951457A
Application number: US728166A
Authority: US
Inventors: Jr Strickland Kneass
Original assignee: Morgan Construction Co
Current assignee: Siemens Industry Inc
Priority date: 1958-04-14
Filing date: 1958-04-14
Publication date: 1960-09-06
Anticipated expiration: 1977-09-06

Description

Sept. 6, 1960 s. KNEASS, JR

EJECTOR STACK 2 Sheets-Sheet 1 Filed April 14, 1958 INVENTOR. StTicK land Kneass J1:

S. KNEASS, JR

Sept. 6, 1 96 0 EJECTOR STACK 2 Sheets-Sheet 2 Filed April 14, 1958 INVENTOR. Strickland Kneass J1:

H 07'' e y EJECTOR STACK Strickland Kneass, Jr.,- Worcester, Mass., assignor to Morgan Construction Company, Worcester, Mass., a corporation of Massachusetts Filed Apr. 14, 1958, Ser. No. 728,166

6 Claims. (Cl. 110-160) This invention relates to an ejector stack and more particularly to apparatus arranged to withdraw hot gases from a regenerative furnace or the like.

In the operation of high temperature furnaces, such as the open hearth furnace, it is common practice to provide the necessary draft for the withdrawal of gases by using an ejector stack of the type shown and decribed in the patent of Kneass No. 2,397,870. There are situations in which it would be desirable to increase the eificiency of such a stack. First of all, in the initial design of equipment it is always beneficial to reduce the cost; in the case of the ejector stack, increasing the efliciency means a reduction in the size of the fan motor necessary to obtain a given capacity and a decrease in the power consumption. Secondly, in many-installations the furnace is being operated well above its original design limits; this increase in the amount of fuel fired results in an increase in the temperature of the waste gases, since the regenerator capacity remains the same. This also has a tendency to increase the velocity of the waste gases being pushed through the throat of the ejector by the air from the nozzle. In order to operate an ejector efiiciently, it is necessary that there be a very definite differential between the velocity of the ejection air and the velocity of the gas. As the temperature and volume of the waste products are increased, with a given ejector stack this difierential tends to be reduced and both the efiiciency and the pumping capacity fall off. :In many cases, of course, this effect could be overcome by the use of a higher pressure fan, delivering air at increased volume and increased velocity; the cost and operation of such a fan would be higher than that of the original fan. There are certain cases, however, where it is practically impossible to do this without going to abnormal horsepower on the ejector fan motor. These and other difiiculties experienced with the prior art apparatus have been obviated in a novel manner by the present invention.

It is therefore an outstanding object of the invention to provide an ejector stack of increased efiiciency.

Another object of this invention is the provision of ap paratus for use with an ejector stack to permit it to handle greater volumes of gases with increased temperatures.

A still further object of the present invention is the provision of an ejector stack of increased efficiency that is simple and inexpensive to manufacture, which is simple to maintain, and which is capable of a long life of useful service. 1

Another object of the instant invention is the provision of an ejector stack apparatus having increased capacity and having automatic means for regulating its operation to obtain a maximum efliciency over a wide range of gas temperatures and velocities.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best Patented Sept. 6, 1860 understood by reference to certain of its structural forms, as illustrated by the accompanying drawings in which:

Figure 1 is a vertical sectional view of apparatus embodying the principles of the present invention, and

Figure 2 is a schematic view of control elements associated with the apparatus.

Referring first to Figure 1, wherein are best shown the broad features of the invention, the ejector stack, indicated generally by the reference numeral it is shown in conjunction with a vertical passage 11 which receives the upward flow of the hot gaseous products of combustion from one of the regenerative checkers of a furnace, not shown. The passage 11 is provided with an upper converging portion 12 which is connected to an upwardly-converging lower portion or nozzle portion 13 of the stack. The upper end of the portion 13 is connected to the lower end of a transition portion 14 to the upper end of which is connected an upper portion 15 having an upwardly-diverging form. The passage 11 is provided with a lining 16 of a suitable heat-resisting material such as fire-brick or the like.

The upper end of converging portion 12 is connected to a tubular element 17 which converges slightly in the upward direction. The upper end of the element 17 lies very close to the inner surface of the lower portion 13 of the stack. A duct 18 leads from the lower portion 13 to the outlet of a forced-draft fan 19. A duct 21 enters the portion 12 to introduce combustion air downwardly into the passage 11 when the regenerative cycle is reversed. A slide valve or damper 22 serves on occasion to close the stack, while a similar slide valve 30 is provided in the duct 21.

Mounted centrally of the converging portion 12 in the upper part thereof is a group of four

fog nozzles

23, 24, 25 and 26 each having a

separate pipe

27, 28, 29 and 31, respectively, leading in through the wall. Surrounding the nozzles is a cooling jacket 32 having an incoming water pipe 33, and a drainage water pipe 34. The jacket is provided with an upstanding flange to surround and protect the delicate nozzles.

Referring now to Figure 2, it can be seen that the ejector stack 10 is normally used in conjunction with a similar stack 35, the stacks being alternately opened and closed to bring the regenerative checkers, not shown, into operation in the usual way. The stack 35 is provided with fog nozzles and water cooling apparatus in the same manneras the stack 19, so that the detailed description will be limited to the apparatus associated with the stack it). The

pipes

27, 28, 29 and 31 are provided with

solenoid valves

36, 37, 38 and 39, respectively, and are all connected to a water supply pipe 41 leading through a solenoid valve 42 to a pump 43. The inlet of the pump is connected through a normally-operated shut-off valve 44 to a main water supply line 45. The incoming water pipe 33 is connected to the line between the pump 43 and the valve 44, the pipe 46 having a shut-oft" valve 47 located therein. The drain pipe 34 is connected to a main drain line 48. A pressure regulating valve 49 is connected to the line 41 between the pump 43 and the valve 42. A controller 51 is connected by

lines

52 and 53 to a source of electrical power, not shown. A pyrometer 54 is mounted in the stack 10 and is connected by a lead 55 through a reversing switch 56 to the controller 51. A lead 57 connects the controller 51 to the pressure regulating valve 49.

Leads

58, 59, 61 and 62 are connected to the

solenoid valves

36, 37, 38 and 39, respectively, and to corresponding solenoid valves associated with the fog nozzles of stack 35. The apparatus provided for the stack 35 exactly duplicates that connected with the stack 10; for instance, a solenoid valve 63 is connected in the water line leading to the fog nozzles of the stack 10 and a reversing switch 64 is connected in the line leading to its pyrometer 65. The regenerative cycle is controlled by a conventional timing apparatus, not shown, which reverses the gas flow; this apparatus is connected to the reversing switches 56 and 64. These switches are always conditioned so that one is open while the other is closed; when the timing apparatus reverses the gas flow, it also reverses the condition of these switches. Similarly, the

V solenoid valves 42 and 63 are oppositely conditioned and are connected to the timing apparatus to reverse their condition when the gas flow is reversed. A controller 51 is connected by

lines

52 and 53 to a source of electrical power, note 42 and 63 are oppositely conditioned and are connected to the timing apparatus to reverse their condition when the gas flow is reversed. The controller 51 is constructed in a well-known manner to cause electrical current to pass through the

lines

59, 58, 61 and 62 in re sponse to signals from the pyrometer 54 or 65 indicative of gas temperature. The controller permits current to pass continuously through the line 58, to pass through the line 59 only when the pyrometer indicates that the gas temperature exceeds a first predetermined level, to pass through the line 61 only when the gas temperature exceeds a second higher level, and to pass through the line 62 only when the gas temperature exceeds a third, highest level.

The operation of the apparatus will now be understood in view of the above description. Let us assume that the slide valve 22 of the stack is open and the corresponding valve of the stack 35 is closed; the valve 30 of the stack 10 is closed, while the corresponding valve of the stack 35 is open. Thus, gas from one regenerative checker is passing upwardly through the stack 10 and combustion air is passing downwardly through the lower part of the stack 55 to the other checker. Air originating in the fan 19 enters the chamber formed by the lower portion 13 and the element 17 and passes upwardly through the narrow gap at the upper end of the element 17. The ejector action produced by this flow of air draws gas upwardly and carries it up the stack. Water is projected upwardly from the nozzles in the form of a fine spray or fog; the water is evaporated and the vapor mixed with the gases. The number of nozzles operating 'depends on the temperature of the gases as measured by the pyrometer 54 which transmits a signal indicative thereof through the line 55 to the controller 51. The switch 56 is opened, while the switch 64 is closed; the valve 42 is open and the valve 63 is closed. Therefore, it is the pyrometer 54 which energizes the controller 51 and Water can pass only to the fog nozzles in the stack 10. The controller causes current to pass through a certain number of the

lines

58, 59, 61 and 62, depending on the gas temperature. The higher the temperature, the more lines energized. Thus, a corresponding number of the

solenoid valves

36, 37, 38 and 39 are opened and the same number of fog nozzles are supplied with water. Even though some of the solenoid valves associated with the fog nozzles of the stack 35 are opened at this time, it will be understood that the closed condition of the valve 63 prevents flow of water therethrough.

When the timing apparatus reverses the regenerative cycle, the slide valve 22 is closed and the valve 30 is opened, so that combustion air flows from the duct 21 and downwardly into the checkers associated with the stack 10; the products of combustion now flow upwardly through the stack 35. The switch 56 is closed, while the switch 64 is opened, so that only the pyrometer 65 operates the controller. At the same time the timing apparatus closes the solenoid valve 42 and opens the valve 63, so that, irrespective of the conditions of the solenoid valves associated with the fog nozzles, water will only flow to nozzles remains constant at any given setting, but it provides for fine graduations of water flow to the nozzles with variations of gas temperature. It can be seen, then, that the

solenoid valves

36,37, 38 and 39 provide for large changes of gas temperature, while the adjustment of the pressure regulating valve provides for regulation of the flow between the ,broad control points set by the solenoid valves.

For the purpose of showing the beneficial effect of using a water spray nozzle for cooling the. waste gases from a furnace when pumped through an ejector to produce a furnace draft, let us assume the following condition:

Let the temperature of the gases leaving the furnace be 1100 F. andthe draft required be.2" of water suction in the stack below'the ejector, exclusive of any natural draft that may be present. Furthermore, let the quantity of gases be 100 cubic feet per second at standard conditions (30 Hg and 60 degrees.F.). The gas analysis by volume shows 6.6% of CO 13.3% of H 0, 73.6% of nitrogen, and 6.5% of oxygen. The weight of the gases is 7.4 lbs. per 100 cubic feet; this is obtained by multiplying the amount of each gas in the 100 cubic feet by its specific weight at standard conditions, as

. obtained from the standard tables, and adding the weight thus obtained. The conditions represent those frequently met in practice.

For the purpose of calculating the fog nozzle cooling, let us assume that enough water will be supplied to cool the furnace gases from 1100 degrees'F. to 400 degrees F. Now, 100 cubic feet of the gases with the assumed analysis at 1100 F. will contain 2100 B.t.u. above the heat content at 60 F. This figure is obtained by multiplying the number of cubic feet of each gas in the 100 cubic feet by the number of B.t.u. required to raise a cubic foot of the gas 1 F. (as obtained from standard tables) by the number of degrees above standard temperature (60 F.) and then adding the separate heat values thus obtained. If the gas is at 400 F. the heat content over that at 60 F. would be 670 B.t.u. This leaves us 1433 B.t.u. to be absorbed by the Water.

Let us also assume that the water would be projected into the gas stream at 70 F. and that it would be transformed into steam at atmospheric pressure. The temperature of the saturated steam would be 212 F. and would have to be superheated 188 to raise it to 400 F. From the steam tables, the total heat content of the superheated steam at 400 F. would be 1240 B.t.u. per pound, while that at 70 F. is 38 B.t.u. per pound, so that the difference, 1202 B.t.uper pound is available for cooling the gases.

Since 1433 B.t.u. must be absorbed to lower 100 cubic feet of the gases from 1100 F. to 400 E, it would require 1433/1202 or 1.192 lbs. of water per 100 cubic feet of gas ejected. Since the air passing through the ejector nozzle must pump the mixture of gas and superheated steam, the mixture consists of 7.4 lbs. of gas and 1.2 lbs. of steam or a total of 8.6 lbs. of gaseous fluid at 400 F. With a requirement of a draft of 2" of water and the weight of a cubic foot of the dry gas at 400 F. being .0417, the total head against which the gas will be pumped is or 250 feet of gas at 400 F. This means that the theoretical work required to deliver the gas from furnace pressure to the atmosphere is 250x86 or 2150 foot I pounds per second.

If no water cooling is used, it is still necessary to pump 7.4 pounds of gas, which gas at 1100 F. has a volume of 300 cubic feet. Since the necessary draft is still 2" H 0 and the weight of the gas is now .025 pound per cubic foot, it is necessary to pump 7.4 pounds of gas from the furnace against a head of or 416 feet or gas at 1100 F. The work that is required to do this is, therefore, 416 7'.4 or 3070 foot pounds per second.

It is evident then that the power required to pump the gas without water cooling is 3070/2150 or 143% of that required when the principles of the present invention are used.

Furthermore, due to the fact that the gas at 400 F. is somewhat denser, the efliciency of the ejector is somewhat higher and the work done by the air jet in pumping the cooled gas is considerably less. In ordinary practice, the work required to pump the gas at 1100 F. would be approximately 175% of that required to pump the cooled gas and vapor mixture. In addition, the size of the ejector itself may be materially reduced. It is common practice to use a velocity of 140 feet per second in the throat of the venturi or diffuser. For gas cooled to 400 F., it would require an area of 1.475 square feet in the gas passage, while the cross-sectional area with gas at 1100 F. would be 2,145 square feet; the reduction in size of the entire apparatus with the use of the present invention will be evident. The areas are obtained by dividing the volume of gas in each case by 140 feet/sec. The area for the water cooled situation is 20615/140 or 1.475 sq. ft. where the 206.5 cubic feet/ sec. was obtained by adding the separate volumes of the water and the gas at 400 F. The Water volume is 1.192 lbs. 34.83 cubic feet per pound of steam at 14.7 p.s.i. pressure and 188 F. superheat (from steam tables) or 41.25 cubic feet/ sec. The gas volume is the selected volume at standard conditions multiplied by the ratio of the absolute temperatures:

and the throat area equals 300/140 or 2.145 sq. ft. As 100 p.s.i. water is sufiicient to give the necessary high velocity and breaking up of the water spray, the actual Work required to eject the water is 277 foot pounds per second, which is very much less than the difference between the work required to pump the uncooled gas and the work required to pump the cooled gas.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent rs 100 165.25 cubic feet/sec.

1. Apparatus for the drafting of hot gases, comprising a passage for the gases, an upright stack communicating at its lower end with the passage and open at its upper end to the atmosphere, a nozzle to discharge cool air only upwardly into the lower portion of the stack, whereby the gases are entrained and carried upwardly through the stack, a duct leading to the nozzle, a fan to supply air to the duct, water nozzles located at the lower portion of the stack, means supplying water at considerable pressure to the water nozzles, and an automatic regulator arranged to increase or decrease the flow of water to the water nozzles in accordance with increase or decrease, respectively, or the temperature of the gases, the water being introduced into the gases upstream of the area of introduction of the air to the gases.

2. Apparatus for the drafting of hot gases, comprising a passage for the gases, an upright stack communicating at its lower end with the passage and open at its upper end to the atmosphere, a nozzle to discharge cool air only upwardly into the lower portion of the stack, whereby the gases are entrained and carried upwardly through the stack, a duct leading to the nozzle, a fan to supply air to the duct, a plurality of fog nozzles located at the lower portion of the stack, means supplying water at considerable pressure to the fog nozzles, a valve associated with each fog nozzle and operative to shut oif the flow of water to its nozzle, and an automatic regulator arranged to control the condition of the valves to increase or decrease the flow of water to the fog nozzles in accordance with increase or decrease, respectively, or the temperature of the gases, the water being introduced into the gases upstream of the area of introduction of the air to the gases.

3. Apparatus for the drafting of hot gases, comprising a passage for the gases, an upright stack communicating at its lower end with the passage and open at its upper end to the atmosphere, a nozzle to discharge cool, air only upwardly into the lower portion of the stack, whereby the gases are entrained and carried upwardly through the stack, a duct leading to the nozzle, a fan to supply air to the duct, water nozzles located at the lower portion of the stack, means supplying water at considerable pressure to the water nozzles, a'pressure regulating valve located between the said means and the said water nozzles, and an automatic regulator arranged to adjust the setting of the pressure regulating valve so that the regulated pressure of the Water is so adjusted, the regulator so acting to increase or decrease the flow of Water to the water nozzles in accordance with increase or decrease, respectively, or the temperature of the gases, the water being introduced into the gases upstream of the area of introduction of the air to the gases.

4. Apparatus for the drafting of hot gases, comprising a passage for the gases, an upright stack communicating at its lower end with the passage and open at its upper end to the atmosphere, a nozzle to discharge cool air only upwardly into the lower portion of the stack, whereby the gases are entrained and carried upwardly through the stack, a duct leading to the nozzle, a fan to supply air to the duct, a group of water nozzles located at the lower portion of the stack, means supplying water at considerable pressure to the water nozzles, a hollow jacket surrounding the group of water nozzles to protect them from the gases, means causing water to flow through the jacket, and an automatic regulator arranged to increase or decrease the flow of Water to the water nozzles in accordance with increase or decrease, respectively, or the temperature of the gases, the water being introduced into the gases upstream of the area of introduction of the air to the gases.

5. Apparatus for the drafting of hot gases, comprising a passage for the gases, an upright stack communicating at its lower end with the passage and open at its upper end to the atmosphere, a nozzle to discharge cool air only upwardly into the lower portion of the stack, a duct leading to the nozzle, a fan to supply air to the duct, a plurality of fog nozzles located at the lower portion of the stack, means supplying water at considerable pressure to the fan nozzles, a shutoff valve associated with each fog nozzle and operative to terminate the flow of water to its nozzle, a pressure regulating valve located between the said means and the said fog nozzles, a hollow watercooled jacket surrounding the fog nozzles to protect them from the gases, and an automatic regulator arranged to control the condition of the shutoff valves and adjust the setting of the pressure regulating valve so that the regulated pressure of the water is so adjusted, the regulator .so acting to increase or decrease the flow of water to the wardly into the lower portion of the stack, whereby the gases are entrained and carried upwardly through the stack, means to supply air to the duct, a plurality of water nozzles located to project water into the gases approaching the air nozzle, means supplying water at considerable pressure to the water nozzles, a solenoid-operated shutofi valve associated with each water nozzle and operative to terminate the flow of water to its nozzle, a pressure regulating valve located between the said means and the said water nozzles, a pyrometer located in the flow of gases, a hollow water-cooled jacket surrounding the water nozzles to protect them from the gases, and a controller arranged to receive an indication of gas temperature from the pyrometer, the controller acting to regulate the" conditions of the shutoff valves and to adjust the setting of the pressure regulating valve so that the regulated pressure of the water is so adjusted, the controller thus acting to increase or decrease the flow of water to the water nozzles in accordance with increase or decrease, respectively, or the temperature of the gases, the water being introduced into the gases upstream of the area of intro duction of the air to the gases.

References Cited in the file of this patent UNITED STATES PATENTS 882,767 Moran et a1. Mar. 24, ;1908 1,236,793 Warman Aug. 14, 1917 1,237,791 Kitchel Aug. 21, 1917 1,410,718 Prat Mar. 28, 1922 i1,736,675 Steese Nov. 19, 1929 2,542,684 Laverdisse et a1. Feb. 20, 1951 2,722,372. Edwards Nov. 1, 1955 M'aiman Feb. 28, 1956