US2115548A - Heating - Google Patents

Description

April 26, 1938. N; c. ARTSAY HEATING 2 Sheets-Sheet 1 Filed April 27, 1955 INVENTOR.

NICHOLAS CARTJAY ATTO EY.

April 1938. N. c.-ARTsAY 2,115,548

HEATING I Filed April 27, 1935 2 Sheets-Sheet 2 INVENTOR. /V/CHOL/45 6'. 427124) ATTORN Patented Apr. 26, 1938 r HEATING Nicholas 0. Artsay, Valhalla, N. Y., a... to Foster Wheeler Corporation, New York, N. Y., a

corporation of New York I Application April 2'1, 1935, Serial No. 10,572

4 Claims. (01; 122-43) This invention relates to heating processes and apparatus.

In many industrial plants, especially chemical plants, there is a need for heating processes in the range of 500 to 700 F. in which the temperature oi. heating elements must be constant and uniform throughout. This result,

in the lower range of temperature, is usually attained by condensing steam. However, the higher temperature range involves steam pressures from 650 to 3000 lbs. per 'sq. in. which necessitates special boiler installations and large expense. To reduce the operating vapor pressures necessary, other fluids or materials such as the l5 diphenyloxldes, have been employed. In most cases, the high temperature range processes are of intermittent character and considerable inconvenience is experienced in. starting up the special boiler after each shut down. Instead of employing special boilers for this purpose, it has .been found more desirable to draw the needed amounts of heat from steam or other vapor produced by a boiler already on the line. There are several known methods of incorporating high pressure steaming elements in ordinary low pressure boilers and 'these arrangements throttle down the high pressure steam to the pressureinthe mains when the higher pressures are not needed.

' This involves the installation of a high pressure feed pump and the contamination of the high pressure heating surfaces with the boiler feed water which may be satisfactory for the low pressure boiler'but is undesirable for the high pres-' sure elements. The high pressure feed pump can 5 be eliminated, if desired, to make the circuit a closedcircuit and return the condensate by gravity, however, the throttling of unneeded steam is.

then impossible so'that another place of condensation must be provided. If this place of con- 40 densation is a coil in the boiler drum, the high pressure heating elements should be placed considerably above the boiler drum to provide for the gravity return of condensate. This involves great difliculties in a great "majority-of boiler designs 45 gfifi'cannot be done at all with boilers already steam and also to any other heat carrying fluid used in the system. A condensate pump can be installed which is located in a sumclently low 50 position to draw the liquid and return it to the heating elements, but if water is used as a fluid, the pump must be constructed to stand the high pressure and necessarily will be expensive. Moreover, the circulating means must always be op- "sting o to insure the reliahil tv of bo ler oner- This consideration applies both to water ation and to comply with the boiler statutes, at least two circulating pumps will be required.

The present invention provides a novel heating method and apparatus which overcomes all these difficulties. In general, the arrangement 5 includes a fluid heater placed outside an ordinary heater, such as a steam boiler, the fluid to be heated and vaporized being circulated by a pump through the tubes in one or more circuits.- The fluid or other material to be heated may be 10 any substance having a sufllciently high boiling point for the purpose desired. Such materials will include diphcnyloxides, 'or a mixture of diphenyl and diphenyloxide, mercury, high boiling point oils, and concentrated solutions of certain salts. 15 Part of the hot gases passing through the boiler or other heater is diverted into the fluid heater and after being cooled by giving up heat to the fluid, it is returned into a'lower temperature zone of the boiler or its eccnomizer or air heater. When the fluid is only partly vaporized in the heater, the arrangement preferably includes a separator which returns the liquid phase to the pump, and the vapor is conducted to the place of heat consumption. A distributing valve is em- 25 played to divert part of the vapor into cooling processes after which the steam is contaminated and the condensate made worthless for further use. The safe operation of a high pressure steaming element subject to hot gases requires the use of distilled water for feeding, which is.

often unavailable. I For these cases, thearrangement embodying the invention may include a drum in which high pressure steam is generated by means of heating elements in which the heating vapor is condensed. This arrangement eliminates thedanger of overheating or burning the high pressure tubes.

The heating process and apparatus of the invention and its novel features'will be understood from the'following description when considered in connection with the accompanying drawings, in

which:

Fig. 1 is a more or less diagrammatic view in vertical section, of apparatus embodying the inventlon; and

Fig. 2 is a similar view showing another form of the invention.

Like reference characters refer to the same or similar parts in both views.

The invention will be described and illustrated in connection with steam boilers and with part of the products of combustion produced in the furnaces of the boilers being utilized to heat the fluid by means of which heat is supplied to the process or other desired points or zones. Itwill be understood however that the invention amt limited in its application to steam boilers but that it also may be utilized in connection with heaters in general or other sources of heat.

Referring to the form of invention shown in Fig. 1, reference character l0 designates a straight tube stoker fired boiler of conventional design. Any other boiler design may be employed, if desired. The boiler shown has a furnace li, a steam and water drum l2, banks of boiler tubes l3 and an economizer i4 in a flue IS. A superheater I6 is located in the first of the three passes l1, l8 and [9. During operation of the boiler, part of the combustion gases are withdrawn from the furnace at 20 and are led through a refractory lined duct 2i into a two-pass fluid heater 22. It is understood that the gases may also be withdrawn from any other convenient high temperature zone of the boiler. The heater 22 has a heating coil 23 extending through both passes, and the tubes in the cooler second pass are fltted with extended surfaces 24. Obviously, the heater may have a single pass or more than two passes and the tubes of the heating coil may all be bare or may all be fltted with extended surfaces. After being-drawn through the heater, the gases enter 'an outlet duct 25 and are delivered by a fan 26 into an outlet duct 21 which discharges into the flue l5 below the economlzer. A circulating pump 21' takes the 'fluid to be heated in the liquid phase from a surge tank 23 and delivers it through pipe 23 having a check valve 33, and pipe 3| to heating coil 23. After being vaporized to the extent desired incoil 23, the fluid enters a vapor separator 32. The liquid Phase thrown down in the separator 32, returns through a trap 33 and pipe 34 to the surge tank 23, while the separated vapor flows through pipe 36 into a distributing valve 36 having a piston 31 which controls the inlets to pipes 33 and 33, so that when the inlet to one of these pipes is closed the other is open. Valve 36 is controlled in response to the pressure of-the fluid in pipe 33 and is normally urged in a position to close the inlet to pipe 33 by a spring 43. lfrom the valve 34 the vapor may be led through pipe 33 to the condensing coil 4! placed in the boiler drum and/or to the process heating coils 42 shown as a bank of tubes heating a fluid in a tank 43 through pipe 33 and control valve 44. The process heating is controlled by the valve 44 and a check valve 46 in the fluids condensate returnpipe 44 which connects through pipe 41, loop seal 43 and pipe 34 with the surge tank. The fluids condensate in the boiler drum coil v surge tank through pipe 43 which connects with pipe 41. The heater 22 produces an amount of fluid's vapor in proportion to the amount and temperature of the gases drawn through it? The boiler may be running at variable load and hence the amount of gases for a given amount of heat extraction will be variable also. The amount of heat extraction as manifested by the vapor pressure may be regulated inany known manner. In thisinstaneathevaporpressureimpulseis trans- 4'i is returned also to the.

ferred by the pipe 50 to a pressure responsive device 5l which controls the pneumatically actuated cylinder 52 which in turn operates and controls the damper 53 in duct 21. If desired, the pressure responsive device 5| or the like may be arranged to control the speed of the fan 26. For any given amount of heat extraction, the vapor pressure in the fluid circuit will depend on the proportion of vapor flowing into the coil 42 and the coilv 4!, the latter being surrounded by boiler water at a substantially lower temperature than that of the process fluid in the tank 43. For proper heating effect in the tank 43, the pressure of vapor in the pipe 39 before the process valve 45, is maintained constant by the distributing valve 36. Whenever vapor pressure in the pipe 39 decreases, the valve 36 reduces the flow into the coil 4| and increases the flow to the coil 42 and vice versa. Thus during the operation the vapor pressure in the coils 4i and 42 will be tending to be difierent, but substantially lower in the former. To make the control of distribution more effective, a slight over-pressure will be maintained before the distributing valve 36 by proper setting of the device. When the process valve 44 is open, the vapor pressure in the fluid condensate lines 46, 49, and 41 and the surge tank 23 will be equal to the pressure in the process coil 42 which means that the return of condensate fromthe coil 4i through the pipe 49 will be impeded and consequently the coil 4| will be flooded with condensate up to a certain level when the remaining vapor condensing surface of high heat transfer rate will be sufllciently small to give an undercooling to the condensate in the coil 4 i, and a reduced flow of vapor to maintain the vapor pressure and effect the return of condensate. When the process valve 44 is closed at the end of the process operation, the vapor pressure in pipe 33 will rise and the valve 36 will close the inlet to the pipe 33 and open more the inlet to the pipe 33 leading to the coil 4|. This will result in the purging of the coil 4i and the restoration of the full heat transfer capacity by means of which all of the heat extracted from the boiler gases some of the gases will nevertheless pass the heater 22 and the vapor generated at such times will be condensed in the coil 4|. Shouldit be desired to shut down the circulating pump 21', a by-pass 6! controlled by a valve 56 and which connects ,pipe 41 at loop seal 43 with pipe 3i provides a circuit of natural circulation for the fluid. Qheck valve 33 will prevent flow into the surge tank through the pump 21' when the pump is not operating.

Since most of the high boiling point substances which are suitable are solids at moderate room temperatures, when the boiler is shut down, the fluid is drained to the surge tank 28 from the heater, by opening the valve 51 in line 53 which connects pipes 23 and 34. In the surge tank, the substances can remain solid without inconvenience and can be melted when needed either by the higher boiler room temperature or by using a small steam coil around the tank 23.

In the form of the invention shown in Fig. 2, a boiler of the Stirling type is employed. This boiler is designated generally 30 and has afur-' nace 8i, drums 32, 43,34 and 46, which are. connected by boiler tubes 63 in the usual manner. 76

" The combustion gases after flowing over the boiler tubes, are delivered to an air heater i1 through a duct 68 and thence out to a flue pr stack. High pressure steam, for instance at 1500 lbs. per sq. in., is generated in the drum I placed in a vertical position preferably. The drum is fitted with blow down valves "II at the bottom to purge it from mud and concentrated solids in the feed water which enters through the valve I2 in pipe 13. The steam generated in the drum is taken out through pipe 14 controlled by a stop valve I5. Heat is. supplied for vaporizing the- I water in the drum 10 by condensing the vapor of diphenyloxideor other suitable substance in a heating coil 16 disposed in the drum and connected with the vapor and condensate pipes. Due to the relatively low temperature inside the tubes of the coil Hi, there is no danger'in scale accumulation on their outer surface and consequently ordinary feed water can be'supplied for high pressure steam generation. The degree of scale accumulation will be observable through the vapor pressure of the substance employed (or temperature diiference) for a given high pressure steam output. The method of descaling these tubes will be hereinafter described.

The'pump 21' circulates diphenyloxide or other substance through the heater 22 which is supplied, by va controlled amount of furnace gas drawn through the heater by the fan 26, ashereinbefore described. The vapor and liquid mixture is passed through the separator 32 and the separated liquid is returned to the surge tank 28, while the vapor is led to the distributing valve 38.

.In this case, the distributing valve is responsive to and is regulated to maintain the desired pressure of steam in the 'drum Ill. Whenever steam. pressure in the drum changes, the valve 36 reduces or increases the flow of vapor in the tubes I6 and at the same time increases or decreases the flow into the coil 4| placed in the water of the boiler drum 62. The fan speed or damper regulator 5|, 52 will maintain the pressure of vapor by changing the how of gases through the heater 22.

, The return of condensate from the coil 4| and heating element 16 is effected in substantially the same manner as described for the form shown in Fig. 1. To comply with the law, a safety valve 11 may be put on the high pressure drum I0 and also on the circuit of the heating substance (not shown) The natural circulation for such times as the high pressure steam is not needed, and both the fan 26 and the circulating pump 21' are shut down, is effected by opening the valve 56in the by-pass pipe 55 which returns condensed vapor from the coil 4| and by loading the valve 36 with a deadweight to open the vapor circuit into the coil 4! and to close the circuit into heat-.-. ing element. If the latter were open, allthe heating substance from the-heater 22 would gradually be drained into the surge tank 28; The shortage of heating substance in the circuit in the condition of natural circulation will be manifested by too high a level in the surge tank 2! and a few seconds operation of pump 21- will serve to restore the shortage. The draining of the heating substance into the surge tank 28 during the long shut downs of the boiler is'effected by the by-pass valve 18 in pipe". The check valve 30 on the pump discharge prevents the emptying of the heater 22 into the tank 28 when operating under-natural circulation.

The descaling. of the heating elements 16 may I claims.

down and damper 53 is closed while the auxiliary damper indicated 59 is opened. Next the valve 8| in line I0 is opened, valve 82 in line is shut, and valve ii in line 38 is opened. In these conditions the heating substance circuit will be divided into two parts: the first part including heater 22, tank 28 and separator 32 will be under higher vapor pressure than the other part which contains both heating elements 16 and 4!. To preclude any untoward rise of vapor pressure; in the isolated flrstpart, cold air is admitted'into the furnace through the damper G9 and the heater 22. The check valves 45 and 84, the closed valve 82 and the opened valve 83 define. a natural circulation circuit comprising both the heating elements I! and 4|. Due to the high temperature diiference between the drum Ill and the boiler drum where the coil 4| is immersed, there will be a quick transfer of heat from the water in drum 10 to the boiler water. Vapor in the tubes 18 will be boiling at a temperature very near to that at which it is condensing in the coil 4|. By opening the valve 83 last and uickly, a substantial quick cooling of' the tubes 16 from the inside will be effected which will be suflicient to break the scale sheath, which-may be afterward removed by opening the blowdown valves 1 I.

If there is a shortage of heating substance in the circuit, it may be restored by,cracking valve 56 such quantities of heat are withdrawn from the said heaters as are,necessary for the requirements in the said heating zone and because any heat after being withdrawn and not utilized is recovered in the heater furnishing the heat initially. v

Since changes may be made in the process and the several steps thereof and in the-forms of apparatus and the several parts thereof which are disclosed herein, without'transcending the principles of the invention, it will be understood that no intention is entertained to limit the invention except by the scope of the appended WhatIclaim is: g

1. Apparatus for supplying heat to a heater comprising a closed circuit for the circulation of a high boiling point heating fluid, said circuit having a portion thereof in said heater, a second heater in said circuit, a steam generator, means for withdrawing and conducting part .of the products of combustion from a high temperature portion of the furnace of said generator to the second heater to heat the fluid flowing therethrough prior to its flow through the first heater. means for returning the withdrawn products of combustion to a low temperature portion of said generator after passage through the second heater, means for controlling the quantity of products of combustionwithdrawn in response to the heating requirements of the first heater,

means for by-passing heated fluid around the first heater, means for controlling the by-pass in response to the heating requirements oi. the first heater, and means for recovering the heat from said by-passed fluid in the steam generator.

2. Apparatus tor supplying heat to a heater from a steam generator at irregular intervals in variable amounts at a temperature level above that of the saturated steam produced in the generator, comprising means for passing a high boiling point heating fluid through a second heater, means for withdrawing a portion of the products of combustion from a high temperature portion of the generator and passing said portion through the second heater to heat the heating fluid to vaporization temperature, means for controlling the quantity of products of combustion so withdrawn from the generator in response to the heat requirements in the heater, means for separating the vaporized and unvaporized portions of the heating fluid, means for distributingthe vaporized portion between the heater and a heat absorbing portion 01' the generator in such manner as to provide the required quantity oi! heat in the heater with excess heat being conducted to said heat absorbing portion of the generator, and means for circulating the unvaporized portion of the heating fluid through the second heater to absorb heat from the products oi combustion passing therethrough at such times as heat is not required to be supplied to said heater.

3. Apparatus for supplying heat to a heater from a steam generator at irregular intervals in variable amounts at a temperature level above that oi. the saturated steam produced in the generator, comprising means for passing a high boiling point heating fluid through a second heater, means for withdrawing a portion of the products 01. combustion from a high temperature portion of the generator and passing said portion through the second heater to heat the heating fluid to vaporization temperature. means for controlling the quantity of products of combustion so withdrawn from the generator in response to the heat requirements in the heater, means for returning the products of combustion so withdrawn to a low temperature point in the generator in the path of flow oi the products of combustion, means for separating the vaporized and unvaporized portions of the heating fluid, means for distributing the vaporized portion between the heater and a heat absorbing portion of the generator in such manner as to provide the required quantity heat in the heater with excess heat being conducted to said heat absorbing portion of the generator, and means for circulating the unvaporized portion of the heating fluid through the second heater to absorb heat from the products oi combustion passing therethrough at such times as heat is not required to be supplied to said heater.

4. Method of descaling tubular elements disposed in contact both interiorly and exteriorly with heated fluids-under pressure and at least partially in the liquid phase, one of said fluids having scale forming constituents, which comprises quickly lowering the pressure upon the other of said fluids to cause partial evaporation of said fluid, thereby cooling said liquid and the tube surface in contact therewith, while main-- taining the pressure and temperature of the other fluid substantially constant, to thereby break the bond between the scale and tuba to remove the scale from the tubes.

NICHOLAS C. ARTBAY.

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