Claims:We claim:
1) A configuration (200) of valves for admission of steam in to a turbo machine, said configuration (200) of valves comprising :
a) a top half outer casing (212) and a bottom half outer casing (214) bolted across a horizontal plane ;
b) a top half inner casing (216) and a bottom half inner casing (218) bolted across a horizontal mating surface and configured within said top half outer casing (212) and said bottom half outer casing (214) respectively, said top half inner casing (216) and said bottom half inner casing (218) provided with a plurality of chambers (232, 234, 236 & 238) therein, said plurality of chambers (232, 234, 236 & 238) in communication with steam through a plurality of connecting pipes (222(a), 222(b), 222(c) and 222(d)) respectively extending from said top half outer casing (212) and coupled to said top half inner casing (216) and said bottom half inner casing (218) ; and
c) a plurality of throttle valves (220(a), 220(b), 220(c) and 220(d)) adapted to pass through said top half outer casing (212) and adapted to mount over said plurality of connecting pipes (222(a), 222(b), 222(c) and 222(d)) respectively, said plurality of throttle valves (220(a), 220(b), 220(c) and 222(d)) controlled by a plurality of control mechanisms (224(a), 224(b), 224(c) and 224(d)) respectively, said plurality of throttle valves (220(a), 220(b), 220(c) and 220(d)) controlling admission of steam to said plurality of chambers (232, 234, 236 & 238) diagonally opposite to each other in respective said top half inner casing (216) and said bottom half inner casing (218) are opened in sequence for uniform thermal distribution and thereby prevent deformation, crack development or shearing of said top half inner casing (216) and said bottom half inner casing (218).

2) A configuration (200) of valves for admission of steam in to a turbo machine as claimed in claim 1, wherein all the plurality of throttle valves (220(a), 220(b), 220(c) and 220(d)) are kept open initially for said top half inner casing (216) and said bottom half inner casing (218) to catch up uniform heat and prevent differential thermal expansion in future inlet of steam.

3) A configuration (200) of valves for admission of steam in to a turbo machine as claimed in claim 2, wherein opening of all the plurality of throttle valves (220(a), 220(b), 220(c) and 220(d)) initially facilitates in ramping up the speed of a rotor gradually to rated rpm.

4) A configuration (200) of valves for admission of steam in to a turbo machine as claimed in claim 1, wherein the steam is admitted sequentially in to said plurality of chambers (232, 234, 236 & 238) step by step to ramp up the power to rated power in steps and for efficiency.

5) A configuration (200) of valves for admission of steam in to a turbo machine as claimed in claim 1, wherein admission of steam in to said plurality of chambers (232 & 236) is done in sequence followed by admission of steam in to said plurality of chambers (234 & 238) in sequence.

6) A configuration (200) of valves for admission of steam in to a turbo machine as claimed in claim 1, wherein said plurality of chambers (236 & 238) of said bottom half inner casing (218) can be coupled to said top half outer casing (212) through said plurality of connecting pipes (222(c) and 222(d)) either from inside or outside.

7) A method of admission of steam in to a turbo machine, said method comprising the steps of:
a) opening of a plurality of throttle valves (220(a), 220(b), 220(c) and 222(d)) controlled by a plurality of control mechanisms (224(a), 224(b), 224(c) and 224(d)) respectively for admission of steam in to a plurality of chambers (232, 234, 236 & 238) of a top half inner casing (216) and a bottom half inner casing (218) to facilitate in uniform heat distribution and to ramp up speed of a rotor gradually to rated rpm ;
b) keeping one throttle valve from the plurality of throttle valves (220(a), 220(b), 220(c) and 222(d)) open controlling admission of steam to one chamber from the plurality of chambers (232, 234, 236 & 238) and closing off all the remaining once the rated rpm of the rotor is reached and thereby ramping up load on the turbo machine to rated power gradually in steps ;
c) opening other throttle valve from the plurality of throttle valves (220(a), 220(b), 220(c) and 222(d)) controlling admission of steam to other chamber from the plurality of chambers (232, 234, 236 & 238) diagonally opposite to the chamber of step (b) ;
d) opening another throttle valve from the plurality of throttle valves (220(a), 220(b), 220(c) and 222(d)) controlling admission of steam to another chamber from the plurality of chambers (232, 234, 236 & 238) ; and
e) opening last throttle valve from the plurality of throttle valves (220(a), 220(b), 220(c) and 222(d)) controlling admission of steam to last chamber from the plurality of chambers (232, 234, 236 & 238) diagonally opposite to the chamber of step (d).

8) A method of admission of steam in to a turbo machine as claimed in claim 7, wherein implementation of said steps (b to e) in sequence facilitates in thermal stress reduction across said top half inner casing (216) and said bottom half inner casing (218).

9) A method of admission of steam in to a turbo machine as claimed in claim 7, wherein chances of deformation, crack development or shearing of said top half inner casing (216) and said bottom half inner casing (218) is arrested by keeping temperature differential within tolerance limits.

, Description:FIELD OF THE INVENTION:
The present invention relates to the field of an arrangement of valves and a method of admission of steam in to a steam turbine. Particularly, the present invention relates to an arrangement of valves and a method of admission of steam for thermal stress reduction in inner casing of a steam turbine.

BACKGROUND OF THE INVENTION:
Generally, Steam Turbine Casings are subjected to high pressure and high temperature steam and in order to withstand high temperature and high pressure, steam turbine casings are to be manufactured either with high strength material or material of greater thickness which ultimately results in high manufacturing cost. So, to reduce the impact of high pressure and high temperature steam on outer steam turbine casings and to reduce thermal stresses on them, steam is admitted in to the steam turbine casing either through nozzle chest or inner casing. The introduction of nozzle chest or inner casing also facilitates in expansion of steam in meridional flow path direction as high pressure steam has low specific volume.

Figure 1(a) illustrates a cross sectional view of a nozzle chest for admission of steam in to a steam turbine.

Figure 1(b) illustrates a side view of throttle valves of a nozzle chest controlled by hydraulic actuated rocker arm.

According to the prior art, there is provided a nozzle chest 100 comprising three nozzle chambers indicated as 12, 14 and 16 through which steam enters a casing of a steam turbine. The entry of steam in to the three nozzle chambers (12, 14 and 16) is controlled by opening and closing of three throttle valves indicated as 22, 24 and 26 which in turn are controlled by hydraulic actuated rocker arm 32.

Depending on the volumetric flow of steam, rated speed of rotor and enthalpy drop, the decision to go with nozzle chest or inner casing is taken. As the nozzle chest 100 is a single unit with three nozzle chambers (12, 14 and 16) and all the three throttle valves (22, 24 and 26) are controlled collectively with the help of hydraulic actuated rocker arm 32, the heat distribution across the nozzle chest 100 is non uniform and concentration of thermal stresses at certain portions of the nozzle chest is very high. So, the chance of deformation or crack development in cases of nozzle chest 100 is high. Therefore, the nozzle chest is sturdy and made up of material with greater thickness.

Typically, the angle of rotation of the hydraulic actuated rocker arm 32 determines the opening/closing of each of the three throttle valves (22, 24 and 26) in sequence.

Several techniques have been disclosed in the prior art for admission of steam in to a steam turbine for uniform thermal stress distribution and improving the efficiency of the turbine.

US Patent no. 3561216 filed on March 19th, 1969 titled “Thermal Stress Controlled loading of steam turbine generators” discloses a method to keep thermal stresses on rotor within tolerance limits during start up and loading conditions or during shift between partial arc and full arc admissions through implementing a logical valve control mechanism. The granted patent teaches about the method of thermal stress distribution on rotors but the granted patent is silent on thermal stress distribution on other turbine components like casings, inner casings etc.,

US Patent no. 4847039 filed on December 11th, 1987 titled “Steam Chest Cross ties for improved turbine operations” discloses a method and apparatus for reducing thermal stress in steam turbines having steam chests with a plurality of linearly-arranged valves controlling respective nozzle chambers. By cross tying selected pairs of the valves and selectively admitting steam through the crosstie, transfers of the turbine from a full arc admission mode to a partial arc admission mode, and vice versa, can be made with a minimum temperature differential. The apparatus and method disclosed in the granted patent for reducing thermal stress is complicated, employed specifically in nozzle chests and occupies a lot of space.

US Patent no. 4325670 filed on August 27th, 1980 titled “Method for admitting steam into a steam turbine” discloses a sequence of activating and deactivating arcuate nozzle chambers of different sizes to achieve maximum efficiency. In this method, activating/deactivating of one large nozzle chamber along with one small nozzle chamber simultaneously is shown for achieving maximum efficiency. The granted patent is focused on achieving efficiency through sequential opening/closing of nozzle chambers but silent on thermal stress reduction.

The present invention finds its application in inner casings parted across the horizontal plane and comprising a plurality of chambers.

Therefore, there is felt a need for development of valves arrangement and a method of admission of steam in to a turbo machine to overcome the drawbacks of the prior art and thereby keeping thermal stresses on inner casings within tolerance limits.

OBJECTS OF THE INVENTION:
An object of the present invention is to provide an arrangement of valves.

Another object of the present invention is to provide a method of opening the valves for uniform heat distribution.

One more object of the present invention is to keep thermal stresses on inner casing within tolerance limits.

Still another object of the present invention is to reduce the chances of deformation or crack development on inner casings.

Further another object of the present invention is to avoid shear movement of the inner casings across the bolted horizontal plane due to thermal stresses.

Yet another object of the present invention is to manufacture simple inner casing at less cost.

SUMMARY OF THE INVENTION:
In accordance with the present invention a configuration (200) of valves for admission of steam in to a turbo machine is provided, the configuration (200) of valves comprising:

(i) a top half outer casing (212) and a bottom half outer casing (214) bolted across a horizontal plane;
(ii) a top half inner casing (216) and a bottom half inner casing (218) bolted across a horizontal mating surface and configured within the top half outer casing (212) and the bottom half outer casing (214) respectively, the top half inner casing (216) and the bottom half inner casing (218) provided with a plurality of chambers (232, 234, 236 & 238) therein, the plurality of chambers (232, 234, 236 & 238) in communication with steam through a plurality of connecting pipes (222(a), 222(b), 222(c) and 222(d)) respectively extending from the top half outer casing (212) and coupled to the top half inner casing (216) and the bottom half inner casing (218); and
(iii) a plurality of throttle valves (220(a), 220(b), 220(c) and 220(d)) adapted to pass through the top half outer casing (212) and adapted to mount over the plurality of connecting pipes (222(a), 222(b), 222(c) and 222(d)) respectively, the plurality of throttle valves (220(a), 220(b), 220(c) and 222(d)) controlled by a plurality of control mechanisms (224(a), 224(b), 224(c) and 224(d)) respectively, the plurality of throttle valves (220(a), 220(b), 220(c) and 220(d)) controlling admission of steam to the plurality of chambers (232, 234, 236 & 238) diagonally opposite to each other in respective the top half inner casing (216) and the bottom half inner casing (218) are opened in sequence for uniform thermal distribution and thereby prevent deformation, crack development or shearing of the top half inner casing (216) and the bottom half inner casing (218).

Typically, admission of steam in to the plurality of chambers (232 & 236) is done in sequence followed by admission of steam in to the plurality of chambers (234 & 238) in sequence.

In accordance with the present invention a method of admission of steam in to a turbo machine is provided, the method comprising the steps of:
(i) opening of a plurality of throttle valves (220(a), 220(b), 220(c) and 222(d)) controlled by a plurality of control mechanisms (224(a), 224(b), 224(c) and 224(d)) respectively for admission of steam in to a plurality of chambers (232, 234, 236 & 238) of a top half inner casing (216) and a bottom half inner casing (218) to facilitate in uniform heat distribution and to ramp up speed of a rotor gradually to rated rpm ;
(ii) keeping one throttle valve from the plurality of throttle valves (220(a), 220(b), 220(c) and 222(d)) open controlling admission of steam to one chamber from the plurality of chambers (232, 234, 236 & 238) and closing off all the remaining once the rated rpm of the rotor is reached and thereby ramping up load on the turbo machine to rated power gradually in steps ;
(iii) opening other throttle valve from the plurality of throttle valves (220(a), 220(b), 220(c) and 222(d)) controlling admission of steam to other chamber from the plurality of chambers (232, 234, 236 & 238) diagonally opposite to the chamber of step (b) ;
(iv) opening another throttle valve from the plurality of throttle valves (220(a), 220(b), 220(c) and 222(d)) controlling admission of steam to another chamber from the plurality of chambers (232, 234, 236 & 238) ; and
(v) opening last throttle valve from the plurality of throttle valves (220(a), 220(b), 220(c) and 222(d)) controlling admission of steam to last chamber from the plurality of chambers (232, 234, 236 & 238) diagonally opposite to the chamber of step (d).

Typically, implementation of the steps (b to e) in sequence facilitates in thermal stress reduction across the top half inner casing (216) and the bottom half inner casing (218).

BRIEF DESCRIPTION OF THE DRAWINGS:
The invention will now be described with reference to the accompanying drawings in which:
Figure 1(a) illustrates a cross sectional view of a nozzle chest for admission of steam in to a steam turbine according to the prior art;

Figure 1(b) illustrates a side view of throttle valves of a nozzle chest controlled by hydraulic actuated rocker arm according to the prior art;

Figure 2(a) illustrates a cross sectional view of an inner casing for admission of steam in to a steam turbine in accordance with the first embodiment of the present invention;

Figure 2(b) illustrates a cross sectional view of an inner casing for admission of steam in to a steam turbine in accordance with the second embodiment of the present invention; and

Figure 3 illustrates a side view of throttle valves of a steam turbine controlled by a plurality of control mechanisms in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
A preferred embodiment will now be described in detail with reference to accompanying drawings. The preferred embodiment does not limit the scope and ambit of the invention. The description provided is purely by way of example and illustration.

Figure 2(a) illustrates a cross sectional view of an inner casing for admission of steam in to a steam turbine in accordance with the first embodiment.

Figure 2(b) illustrates a cross sectional view of an inner casing for admission of steam in to a steam turbine in accordance with the second embodiment.

Figure 3 illustrates a side view of throttle valves of a steam turbine controlled by a plurality of control mechanisms.

In accordance with the present invention, there is provided a configuration 200 of valves for admission of steam in to a steam turbine comprising a top half outer casing 212, a bottom half outer casing 214, a top half inner casing 216, a bottom half inner casing 218, a plurality of throttle valves 220, a plurality of connecting pipes 222 and a plurality of control mechanisms 224.

The top half inner casing 216 and the bottom half inner casing 218 bolted across a horizontal mating surface are configured within the top half outer casing 212 and the bottom half outer casing 214 bolted across a horizontal plane.

The top half inner casing 216 and the bottom half inner casing 218 includes two chambers in each of them indicated as (232, 234) and (236, 238) respectively. The chambers (232, 234, 236 and 238) of the top half inner casing 216 and the bottom half inner casing 218 are in communication with steam by means of a plurality of connecting pipes 222 extending from the top half outer casing 212 and indicated precisely as 222(a), 222(b), 222(c) and 222(d) respectively. The chambers (232, 234, 236 and 238) of the top half inner casing 216 and the bottom half inner casing 218 facilitates in exit of the steam towards first stage of moving blades.

The chambers (236 and 238) of the bottom half inner casing 218 are connected with the connecting pipes 222 either from inside or outside of the top half outer casing 212 as shown in the figures 2(a) and 2(b) respectively.

The plurality of throttle valves 220 indicated precisely as 220(a), 220(b), 220(c) and 220(d) adapted to pass through the top half outer casing 212 and adapted to mount over the plurality of connecting pipes 222(a), 222(b), 222(c) and 222(d) respectively to facilitate in admission/stoppage of the steam to the chambers 232, 234, 236 and 238 of the top half inner casing 216 and the bottom half inner casing 218.

The plurality of throttle valves 220(a), 220(b), 220(c) and 220(d) connected to a plurality of control mechanisms 224 indicated precisely as 224(a), 224(b), 224(c) and 224(d) respectively facilitates in controlling the volumetric flow of steam entering in to the chambers (232, 234, 236 and 238) of the top half inner casing 216 and the bottom half inner casing 218.

Typically, the provision of each individual control mechanism for each of the throttle valves has several advantages in admitting steam in to a steam turbine and gives flexibility in maneuvering the valves like keeping one valve open and other valves closed, keeping one valve closed and other valves open, partially opening one valve and fully opening other valves, keeping two valves open and other valves closed etc.,

Typically, the chambers (232, 234, 236 and 238) of the top half inner casing 216 and the bottom half inner casing 218 can be of same size or different sizes.

The method of admission of steam in to a steam turbine by controlling a plurality of throttle valves 220 to achieve uniform thermal stress distribution in accordance with the present invention is as follows:
The top half inner casing 216 and the bottom half inner casing 218 are bolted across the horizontal plane. Firstly, all the throttle valves (220(a), 220(b), 220(c) and 220(d)) are opened, steam is allowed to flow through all the chambers (232, 234, 236 and 238) of the top half inner casing 216 and the bottom half inner casing 218 and speed of a rotor is ramp up gradually to the rated rpm with the help of volumetric flow of steam. The opening of all the throttle valves (220(a), 220(b), 220(c) and 220(d)) also facilitates in uniform heat distribution across the walls of the chambers (232, 234, 236 and 238) of the top half inner casing 216 and the bottom half inner casing 218 and thereby prevent high temperature differentials in case of steam inlet in to casing of a turbine in future. Secondly, once the rated rpm of the rotor is reached, the throttle valve 220(a) is kept open and the remaining throttle valves (220(b), 220(c) and 220(d)) are closed thereby ramping up loading to rated power in steps by allowing volumetric flow of steam increasingly in steps. Thirdly, the throttle valve 220(c) controlling the admission of steam to the chamber 236 of the bottom half inner casing 218 diagonally opposite to the chamber 232 of the top half inner casing 216 is opened. Finally, the throttle valve 220(b) of the top half inner casing 216 and the throttle valve 220(d) of the bottom half inner casing 218 are opened in sequence.

Typically, the opening of either of the chambers (232 or 234) of the top half inner casing 216 by the throttle valves (220(a) or 220(b)) followed by the opening of diagonally opposite chambers (236 or 238) of the bottom half inner casing 218 by throttle valves (220(c) or 220(d)) facilitates in uniform heat distribution and reduction of thermal stresses.

Typically, the opening of the throttle valve 220(a) of the top half inner casing 216 followed by the opening of the throttle valve 220(d) of the bottom half inner casing 218 or vice versa or the opening of the throttle valve 220(b) of the top half inner casing 216 followed by the opening of the throttle valve 220(c) of the bottom half inner casing 218 or vice versa or the opening of the throttle valve 220(a) of the top half inner casing 216 followed by the opening of the throttle valve 220(b) of the top half inner casing 216 or vice versa or the opening of the throttle valve 220(c) of the bottom half inner casing 218 followed by the opening of the throttle valve 220(d) of the bottom half inner casing 218 or vice versa results in non uniform heat distribution and concentration of thermal stresses which ultimately results in deformation, crack development or shearing of the top half inner casing 216 and the bottom half inner casing 218 across the horizontal mating surface.

TECHNICAL ADVANCEMENTS:
A configuration of valves for admission of steam in to a turbo machine and a method of opening the valves thereof has several technical advantages including but not limited to the realization of:
• an arrangement of valves ;
• a method of opening the valves for uniform heat distribution ;
• a method to keep thermal stresses on inner casing within tolerance limits ;
• a method to reduce the chances of deformation or crack development on inner casings ;
• a method to avoid shearing movement of the inner casings across the bolted horizontal plane due to thermal stresses ; and
• a simple inner casing at less manufacturing cost.

Although the invention has been described herein above with reference to the embodiments of the invention, the invention is not limited to the embodiments described herein above. It is to be understood that modifications and variations of the embodiments can be made without departing from the spirit and scope of the invention.