US3035556A - Multistage steam reheating - Google Patents

Description

May 22, 1962 A. BRUNNER MULTISTAGE STEAM REHEATING 3 Sheets-Sheet 1 Filed March 9. 1959 Fig. 4

T 777 YI'TY' INVENTOR. ALFRED BIPUIVNEIR ATTORNEX May 22, 1962 A. BRUNNER MULTISTAGE STEAM REHEATING 5 Sheets-Sheet 2 Filed March 9. 1959 .E NN u ME 5 HTTO/PNEX May 22, 1962 A. BRUNNER MULTISTAGE STEAM REHEATING 3 Sheets-Sheet 3 Filed March 9. 1959 INVENTOR. ALFRED BRUNNEE'.

United States Patent ()7 3,035,556 MULTISTAGE STEAM REHEATIN G Alfred Brunner, Winterthur, Switzerland, assignor to Sulzer Freres, S.A., Winterthur, Switzerland, :1 corporation of Switzerland Filed Mar. 9, 1959, Ser. No. 798,039 Claims priority, application Switzerland Mar. 12, 1958 1 Claim. (Cl. 122-476) The present invention relates to a method for influencing the condition of the steam leaving resuperheaters operating at different pressures and associated with a live steam generating plant, and to an apparatus for practicing the method.

The method according to the invention includes the step of exchanging heat between the steam at the relatively hot end of one reheater and the steam at the relatively cool end of another reheater.

In the apparatus for practicing the method according to the invention at least one heat exchange surface is provided on one side of which flows steam of the relatively hot end portion of one reheater and on the other side of which flows steam of the relatively cool end portion of the other reheater.

An advantage of the method and apparatus according to the invention is that the heat exchange surfaces of two reheaters operating at different pressures and temperatures can be reduced almost one half of that required for reheaters operating at the same steam temperatures but without heat exchange between the steams of the reheaters, because, with heat exchange between the steams of the reheaters, the steam of one reheater is cooled while the steam of the other reheater is heated or vice versa.

The apparatus according to the invention includes dis tributing valves for distributing the steam onto the heat exchange surface whereby actuation of these valves does not change the sum of the enthalpies of the steam flowing on one side and of the steam flowing on the other side of the heat exchange surface. Actuation of the steam distributing valves, therefore does not cause a disturbance which may affect the control of the heating apparatus of the steam generator with which the reheaters are associated.

The novel features which are considered characteristic of the invention are set forth with particularity in the appended claim. The invention itself, however, and additional objects and advantages thereof will best be understood from the following description of embodiments thereof when read in connection with the accompanying drawing, in which:

FIG. 1 is a diagrammatic longitudinal sectional view of a combustion gas duct containing a two-stage reheater forced flow steam generator including a further modi fication of a two-stage reheater arrangement.

FIG. is a diagrammatic vertical sectional view of a forced flow steam generator equipped with a two-stage reheater arrangement and including automatic controls, FIG. 5a showing detail of the latter.

FIG. 6 is a diagrammatic illustration of a two-stage reheater and heat exchanger arrangement and of control means therefor.

FIG. 7 is a diagrammatic illustration of a modification of the two-valve control mechanism shown in FIG. 6.

3,035,556 Patented May 22, 1962 Referring more particularly to FIG. 1 of the drawing, steam leaving, for example, the high pressure stage of a steam power plant flows through a pipe 1 into one side of an indirect heat exchanger 2. Thereupon the steam passes through a first reheater 3 into a pipe 4 which may be connected to the inlet of a medium pressure turbine, not shown. Low pressure steam, for example the exhaust of a medium pressure turbine, flows on the side of the heat exchange surface of the heat exchanger 2 which side is opposite to the side where the medium pressure steam flows.

The low pressure steam arrives through a pipe 5 and flows through the main part 6 of the second or low pressure reheater wherein the low pressure steam is reheated. The relatively hot low pressure steam is conducted from the end of the reheater part 6 through a pipe 8 to a distributing valve 9 which may be automatically controlled by control signals received from a conductor 10. Such control will be described later. A pipe 11 connects the valve 9 to the low pressure steam inlet of the heat exchanger 2. A pipe 12 connects the low pressure steam outlet of the heat exchanger 2 to an end section 7 of the low pressure reheater. A by-pass pipe 13 connects the valve 9 directly to the pipe 12. The outlet of the low pressure reheater section 7 may be connected by a pipe 14, for example, to a low pressure turbine. An arrow 15 indicates the flow of combustion gas through a flue 16 in which the reheaters are placed. It makes no difference for the system according to the invention whether the distributing valve 9 is connected to the medium pressure side of the heat exchanger 2, i.e. is interposed in the pipe, or is connected to the low pressure side as shown. It the valve 9 is interposed in the pipe 1, the by-pass pipe must be connected to the inlet .of the reheater 3 and pipe 8 must be directly connected to the low pressure side of the heat exchanger 2, in lieu of the pipe 11.

Since the heat exchanger 2 is arranged at the relative cool or inlet portion of the medium pressure reheater 3, the medium pressure steam is heated and the low pressure steam is cooled. If the heat exchange 2 is connected to the relatively hot end, i.e. to the outlet part, of the reheater 3, and steam is taken from the relatively cool part of the reheater 6, the medium pressure steam is cooled and the low pressure steam is heated.

In the embodiment of the invention diagrammatically shown in FIG. 2 a first reheater 17, 18 as well as a second reheater 21, 22 are provided with heat exchangers 23 and 24, respectively, whereby the heat exchanger associated with one of the reheaters is heated by steam from the other reheater. The heating steam taken from the main parts 17 and 21 of the two reheaters is cooled in the respective heat exchanger. The heat exchangers 23 and 24 are located outside of the flue gas channel 25 which is shown in cross section, the combustion gas flowing in a direction normal to the plane of the drawing as indicated by an arrow 26 shown in end view. The two reheaters are placed in the same plane and fill the flue. The two reheaters can therefore be made alike so that they can be interchanged and it is sufiicient to have only one spare reheater.

If the heat supply to both reheaters is the same, the arrangement according to FIG. 2 has the advantage that the heating surfaces of the reheaters are small and can easily be arranged in boiler fines where the space is limited.

Valves 27, 28 regulating the steam flow through the reheaters are preferably automatically controlled as will be described later, whereby a control signal is conducted to actuating means for the valves through a conductor 29. The connection of the reheaters 17, 18 and 21, 22 to the respective heat exchangers is like the one shown in FIG. 1.

The medium pressure steam is supplied to one side of the heat exchanger 23 through a pipe 1 and leaves the reheater 1'7, 18 through a pipe 4. The low pressure steam is conducted to the low pressure side of the heat exchanger 24 through a pipe and leaves the low pressure reheater through a pipe 14.

A control apparatus which will be described later supplies control pulses through a conductor 29 to motor operators for the valves 27, 28 which operate the valves in opposite senses. When the valve 27 opens steam passage to the heat exchanger 23 andcloses the by-pass to the reheater section 2 2, the valve 23 closes passage of steam through the heat exchanger 24 and opens the by-pass to the reheater section 18.-

The valves 27, 28 may be actuated simultaneously or consecutively. If, in the latter case, for example, the flow through both valves 27, 28 was completely stopped, the control apparatus would completely open one valve before completely opening the second valve and vice versa. The control may be so arranged that opening of the valves is effected consecutively and closing is effected simultaneously or vice versa.

The reheater 31 shown in FIG. 3 has portions 32 and 33 wherein two tubes are coaxially placed one within the other. The entire reheater 31 with the portions 32 and 33 is placed in a combustion gas duct 34 through which the combustion gases flow in the direction indicated by arrow 35. Medium pressure steam is conducted through a pipe 1 into the outer tube of the portion 32 wherefrom the steam consecutively passes through a central portion of the reheater and through the outer tube of the portion 33 into a pipe 4.

The low pressure steam arrives through a pipe 5 in which a distributing valve 36 is interposed which directs the low pressure steam either through a pipe 37 into the inner tube of the reheater and heat exchanger portion 33 and therefrom through a pipe 39 to the main part 41 of a low pressure reheater 41, 42, or through a by-pass pipe 43 directly into the low pressure reheater part 41.

The low pressure steam heated in the reheater part 41 flows through a conduit 44 to a valve 45 wherefrom the steam is directed through a pipe 46 into the inner tube of the heat exchanger and reheater portion 32 and therefrom through a pipe 48 into the end portion 42 of the low pressure reheater. The reheated low pressure steam is conducted through a pipe 14, for example, to a low pressure turbine. A by-pass pipe 49 is provided for by-passing the heat exchanger and reheater portion 32 and connecting the valve 45 directly to the pipe 48.

In connection with heat exchangers consisting of tubes coaxially placed within each other and being heated also from the outside, it is preferred to connect the distributing valves to the inner tubes so that steam flows at all times through the outer tubes preventing overheating of the latter.

The distributing valves 36, 45 in FIG. 3 may be operated simultaneously or consecutively or the two operating methods may be combined, as described in connection with FIG. 2.

The steam generator 51 shown in FIG. 4 includes a combustion chamber 52, gas ducts 53, 54 receiving hot combustion gas therefrom, and a flue 55 for conducting the combustion gas into a stack, not shown. The cornbustion chamber 52 is provided with a tilting burner 56 whose position is controlled by a motor operator 57 which responds to signals in a conductor 58. This control will be described later. Combustion air is supplied by a blower 59 having an intake 60.

The walls of the combustion chamber 52 are lined by tubes forming an evaporator 61 which receives feedwater from a feed pipe 62. The steam leaving the evaporator 61 is dried in a water separator 63 and conducted into a high pressure superheater having a first section 64 whose tubes line the walls of the upper part of the combustion chamber 52. The evaporator 61 and the primary superheater 64 are exposed to radiant heat whereas a secondary superheater portion 66, which is connected to the portion 64 by a pipe 65, and reheaters 67 to 69 are heated by convection.

The outlet 92 of the second superheater portion may be connected to a high pressure turbine. A medium pressure primary reheater portion 68 located at the outlet of the gas duct 54 receives medium pressure steam from a pipe 70. A second portion 67 of the medium pressure reheater is arranged upstream of the second high pressure superheater 66 with respect to the flow of the combustion gases.

The outlet of the first portion 68 of the medium pressure reheater is provided with a valve 71 whose motor operator is controlled by control signals arriving through a conductor 72 for selectively conducting steam through a pipe 73 to an inner tube 74 of the steam heat exchanger portion 75 of a low pressure reheater or through a bypass pipe 76 and a pipe 77 directly into the second part 67 of the medium pressure reheater. The outlet 78 of the latter may be connected to a medium pressure turbine, not shown.

Low pressure steam is supplied through a pipe 79 to the outer tube of the steam heat exchanger 75 wherefrom the low pressure steam flows through a combustion gas heated portion 69 of the low pressure reheater whose outlet 30 may be connected to a low pressure turbine, not shown.

Placement of a reheater in the combustion gas stream between portions of a reheater operating at a different pressure and temperature has the advantage that the reheat temperature at the outlets of both reheaters changes substantially to the same extent when the temperature of the combustion gas changes. If the position of the tilting burner 56 is changed, the heat transfer conditions in both reheaters are changed substantially in the same manner.

The condition of the steam at the outlet of the reheaters is characterized by its temperature, pressure, density, and moisture content. If the temperature of the steam at the outlets of the reheaters must be maintained when the load is changed or the pressure of the steam must be changed for producing a desired load, heat exchange between the steams of the reheaters is of advantage. For controlling,

' for example, the outlet temperatures of the reheaters, preferably the sum of the temperatures atthe reheater outlets is used as the controlled variable for producing control pulses for manipulating one or a combination of the following variables: fuel supply, combustion air supply, location of the heat center, feedwater supply. If the fuel supply is controlled, the air supply will be controlled according to the fuel supply, and vice versa, in order to operate at a good combustion efiiciency.

In order to have the desired outlet temperature at each reheater, the difference between the outlet temperatures is preferably used for controlling the heat exchange between the steams passing through the reheaters.

If the reheaters form part of a steam generator which produces superheated high pressure steam which, after expansion, is reheated in the reheater, and if it is desired to control the temperature of the superheated high pressure steam, a variable is preferably manipulated which is not included in the above listed variables. In this case the controlled variable may be the amount of cooling water injected into the high pressure superheater.

FIG. 5 illustrates a steam generating system having two reheaters and a steam heat exchanger at the inlet of the low pressure reheater and heated by steam leaving a first section of a medium pressure reheater. Feedwater is heated in an economizer 103 located in a flue 104. The water is evaporated in an evaporator 106 located in a combustion chamber 107 which is heated by a tilting burner 108. The wet steam produced in the evaporator 106 is dried in a water separator 109 and superheated in a first superheater 110 arranged to receive heat by radiation in the combustion chamber 107. The steam leaving the primary superheater 110 is further superheated in a second superheater 111 located in the flue 104. The steam leaving the second superheater flows through a live steam main 112 to a high pressure turbine 113 whose exhaust is conducted through a first medizm pressure reheater section 114 located in the combustion chamber 107. A pipe 115 conducts the medium pressure steam from the reheater section 114 to a heat exchanger 116 wherefrom the steam is conducted through a pipe 117 to a distributing valve 118 to which a by-pass pipe 119 and, through a pipe 121, a second medium pressure reheater section 122 are connected. The latter receives heat by convection from the combustion gas produced in the combustion chamber 107. The steam reheated in the section 122 flows through a pipe 123 to a medium pressure turbine 124.

The low pressure steam exhausting from the medium pressure turbine 124 flows through a pipe 125 to the heat exchanger 116 and therefrom consecutively through three low pressure reheater sections 126, 127 and 128. The reheated low pressure steam is conducted through a pipe 129 to a low pressure turbine 131.

A thermostat is connected to each of the pipes 123 and 129 for measuring the temperature of the medium pressure and of the low pressure reheated steam. The thermostat connected to the pipe 123 includes a rod 144 of a material whose heat expansion coefficient is smaller than that of the pipe 123. One end of the rod 141 is pivotally connected to the pipe 123 at 136. The second end of the rod 141 forms the fulcrum of a lever 138 one arm of which is pivotally connected to the pipe 123, the second arm of the lever 138 actuating a piston valve 145 through a spring 143. The valve 145 controls flow of a pressure fluid in and out of a cylinder 147 for producing a pressure fluid signal corresponding to the heat expansion of the pipe 123 and thereby to the temperature of the reheated medium pressure steam. The thermostat connected to the pipe 129 is of the same type and produces a pressure fluid signal in a cylinder 148. The signals produced in the cylinders 147 and 148 are conducted through pipes 151 and 152 to the sides of a piston 154 in a cylinder 153. The piston 154, is therefore, moved according to the difference between the temperature of the low pressure steam in the pipe 129 and the temperature of the medium pressure steam in the pipe 123. The movements of the piston 154 are transmitted by a piston rod to the valve 118 for controlling the distribution of the steam from the pipe 115 into the heat exchanger 116 or through the bypass pipe 119 directly into the second medium pressure reheater 122. FIG. 5a is a cross section of the valve 118 and is self-explanatory.

The signals produced in the cylinders 147 and 148 are also conducted through pipes 162 and 158, respectively, to a cylinder 155 in which they act against a spring 164 on the lower sides of connected pistons 157 and 156 so that the energies of the two signals are added. The movement of the double piston 156, 157 is transmitted by a piston rod to the burner 108 for tilting the latter so that the flame in the combustion chamber 107 is directed upward when the sum of the reheat temperatures is too small and vice versa.

The temperature of the live steam is measured by a conventional device 167 for producing a control signal actuating by conventional means, not shown, a valve 166 interposed in a feedwater by-pass pipe 165. When the temperature of the live steam is too high, water passed by the valve 166 is injected into the second superheater 111. If the temperature is normal or too low the valve 166 is closed.

FIG. 6 diagrammatically illustrates an automatic control for a reheater arrangement as shown in FIG. 2. Steam exhausting from a high pressure turbine 113 is consecutively conducted through a heat exchanger 116a, a first medium pressure reheater 114, either through a heat exchanger 116 or directly to a second medium pressure reheater portion 122, depending on the position of a valve 171, and into a medium pressure turbine 124. The steam exhausting from the latter is consecutively conducted through the heat exchanger 116, a first low pressure reheater portion 127, either through the reheater 116a or directly to a second low pressure reheater portion 128, deepnding on the position of a valve 172, and therefrom into a low pressure turbine 131. The valves 171 and 172 are actuated by a common actuating means 200 including a lever 173 which is actuated by a piston 154 in a cylinder 153. The actuating means 200 simultaneously opens one of the valves and closes the other of the valves. The piston 154 is responsive to the difierence of the temperatures of the reheated medium pressure and of the reheated low pressure steam which temperatures are measured by devices like those shown in FIG. 5.

PEG. 7 shows a modified apparatus for actuating the Valves 171 and 172 whereby, upon swinging of the lever 173 in clockwise direction, the valve 171 is actuated against the action of a spring 201 while the position of the valve 172 is not changed, a spring 202 pressing a valve actuating arm 174 against an abutment 175. Swinging of the lever 173 in counterclockwise direction causes actu ation of the arm 174 and of the valve 172 against the action of the spring 202 while the spring 201 moves an arm 176, actuating the valve 171, against an abutment 177. Movement of the lever 173 is transmitted to the arms 174 and 176 by means of a bar 178 having a hook at each end for engaging the arms 174 and 176. Depending on the length of the bar 178 and the distance of its hooks, the valves 171 and 172 are actuated alternatingly, as shown in FIG. 7, or, if the bar is shorter than shown in FIG. 7, the valves are moved simultaneously during a certain period of time or a certain extent of the swinging of the lever 173, or, as shown in FIG. 6, during the entire extent of swinging of the lever 173.

I claim:

Apparatus for reheating steam of different pressures, comprising a reheater for each steam pressure, at least two indirect heat exchangers, each heat exchanger having a heat exchange surface, first conduit means interconnecting a relatively hot portion of a first of said reheaters and a first of said heat exchangers for conducting relatively hot steam along one side the heat exchange surface of said first heat exchanger, second conduit means connected to the inlet portion of a second of said reheaters and to said first heat exchanger for conducting relatively cool steam along the other side of the heat exchange surface of said first heat exchanger, third conduit means interconnecting a relatively hot portion of said second reheater and a second of said heat exchangers for conducting relatively hot steam along one side of the heat exchange surface of said second heat exchanger, fourth conduit means connected to the inlet portion of said first reheater and to said second heat exchanger for conducting relatively cool steam along the other side of the heat exchange surface of said second heat exchanger, a valve interposed in said first conduit means for, controlling the how of relatively hot steam to said first heat exchanger, a valve interposed in said third conduit means for controlling the flow of relatively hot steam to said second heat exchanger, and actuating means interconnecting said valves and including means for simultaneously opening one of said valves and closing the other of said valves and vice versa.

FOREIGN PATENTS German application 1029 388 printed May 8, 1958 (Kl. 14H 4/01).

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