Title of Invention

"A HIGH-TEMPERATURE SHAFT SEAL FOR GAS FLOW DIVERTER IN A COMBINED CYCLE POWER PLANT"

Abstract

The invention relates to a high temperature shaft seal for gas divertor in a combined cycle power plant characterized by a seal housing (1) having a cover plate (2) and a seal element (3) sealing a drive shaft (5) wherein the said element (3) is having a plurality of segments (4) movable readially inwards for adjustment of the gap caused by wear between the drive shaft (5) and the seal (3) and between any two adjacent segments (4) can be closed, the inner diameter being bent at an angle (A) upto 45° towards gas pressure (6) side from the air / bearing side (7) and the inner diameter of the said seal (3) is kept at smaller than the diameter of the drive shaft (5) so that the edge of the seal element (3) sits against the drive shaft (5) surface with finite pressure at the contact line to ensure zero gap at all operating temperature and pressure.

Full Text

The invention relates to a high-temperature shaft seal for gas flow divertor in a combined cycle power plant, having a gas turbine generator and a conventional steam-turbine generator. In a combined cycle power plant, a gas turbine generates electrical power through a generator. The exhaust gases from the gas turbine pass through a Heat Recovery Steam Generator (HRSG), where steam is generated using the waste heat of exhaust gases. The steam is used in a steam turbine-generator system for generation of additional power. This system enhances the thermodynamic efficiency of the cycle significantly. Whenever the steam turbine is not in operation, the exhaust gases of gas turbine are sent out through a chimney. The gas flow divertor is a two-way valve used for directing the exhaust gases to HRSG or chimney. The valve is very large in size (typical area of cross-section being 10 sq.mtr.). The parts of the divertor exposed to the exhaust gases have to withstand temperatures in excess of 550 deg. Celsius. This causes thermal expansions of large magnitude, which have to be taken into account in designing various components of the divertor. An important consideration in design is that loss of heat through the walls of the divertor casing and blade, should be kept minimum by utilising proper insulation. Hence a very efficient sealing system, capable of operating over a large range of temperatures encountered during operation, has to be designed. Blade seals are provided all round the periphery of the divertor blade to ensure sealing. There are disadvantages associated with the present system of divertor blade sealing. One of the main disadvantage with the present system is that sealing efficiency can achieve a maximum of 99.96%. Another disadvantage with the present system of divertor blade sealing is that there are other path of potential leakage which is through the gap between the high-temperature bearings and the drive shaft of the blade. Leakage of hot gas from this path results in heavy loss of heat. Yet another disadvantage with the present system of divertor blade sealing is that leakage of hot gases between the bearings and drive shaft causes heat of the worm gear box. This can result in jamming of the gear box, effecting the functioning of the drive mechanism. Still another disadvantage with the present system of divertor blade sealing is that when the temperature varies, high temperature combine with high compressive stresses cause plastic deformations in the seal element. Further disadvantage with the present system of divertor blade sealing is that the edge of seal wears out due to sliding contact and cannot be adjusted. Thus hot gasses leak out through this gap till the seal element is replaced. Therefore, the main object of the present invention is to provide a very effective high-temperature shaft sealing system required for reliable operation of the drive mechanism. Another object of the present invention is to provide a high-temperature shaft seal for gas flow divertor having a sealing efficiency enhanced to 100%. Yet another object of the present invention is to provide a high-temperature shaft seal for gas flow divertor which is easier to install. Further object of the present invention is to provide a high-temperature shaft seal for gas flow divertor which will stay closed effectively at all operating temperatures by closing the gap constantly. A still further object of the present invention is to provide a high-temperature shaft seal for gas flow divertor which can compensate the effect of wear and increase its useful life. According to the present invention there is provided a high-temperature shaft seal for gas flow divertor in a combined cycle power plant comprising a seal housing having a cover plate and a seal element sealing a drive shaft characterized by the said element is having a plurality of segments movable radially inwards for adjacent of the gap caused by wear between the drive shaft and the seal and between any,two adjacent segments can be closed, the inner diameter being (pent at an angle (A) upto 45° towards gas pressure side from the air/bearing side and the inner diameter of the said seal is kept at smaller than the diameter of the drive shaft so that the edge of the seal element sits against the drive shaft surface with the finite pressure at the contact line to ensure zero gap at all operating temperature and pressure. The nature of the invention, its objective and further advantages residing in the same will be apparent from the following description made with reference to non-limiting exemplary embodiments of the invention represented in the accompanying drawings. Figure 1 shows high-temperature shaft seal assembly. Figure 2 shows the shaft seal as per prior art. Figure 3 shows the high temperature shaft seal with 3 segments as per present invention. Figure 4 shows the sealing of action with the wear of seal element as per present invention. In accordance with the present invention, the divertor consists of a blade/flap assembly mounted on two high temperature bearings. The drive shaft (5) of the blade is rotated by an electrical actuator through a combined bevel and worm reduction gear box system. Blade seals (3) are provided all around the periphery of the divertor blade to ensure a sealing efficiency of 100%. The present system of shaft seal (3) arrangement is shown in Figures 1 and 2. Figures 1 and 2 show a seal housing (1), a cover plate (2) and seal element (3). The seal element (3) is made from sheet of a high temperature alloy with high resilience. A cut is made along the radial direction at one place. The seal element (3) is mounted on the drive shaft (5) by opening it along the radial cut, twisting it and sliding it over the shaft (5). The gap between the shaft (5) and the inner diamter of the seal element (3) is kept as close to zero as possible. However, when the temperature varies, the seal element (3) is at a temperature lower than that of the shaft (5). Thus the edge of the seal element (3) in contact with the drive shaft (5) is subjected to high compressive stresses. Combined with the high temperature, this can cause plastic deformations in the seal element (3). During operation of the divertor, the edge of the seal element (3) is worn out due to sliding contact. Thus a gap is created between the shaft (5) and the seal element (3) because of wear, and thus hot gases leak out through this gap. This gap cannot be adjusted in any way and in such a case the seal element (3) has to be replaced. In view of the above shortcomings, a new shaft seal with the following improvements is proposed in this present invention as shown in Figures 3 and 4. The new shaft seal (3) consists of three segments (4) made of a sheet of high-temperature alloy as against one segment being used in the current design. These segments (4) can be moved radially inwards for adjusting the gap caused by wear during operation. Thus the gap existing between the seal element (4) and the drive shaft (5) and between any two adjacent segments (4) can be closed. The inner diameter of the seal (3) is bent at a small angle (A) and the inner diameter will be kept a little smaller than the diameter of the drive shaft (5). In Figure 4, the right side of the seal (3) is the gas pressure side (6) and in the left in the AIR/BEARING SIDE (4). Thus, the edge of the seal element (3) will sit against the drive shaft surface with some finite pressure (6) at the contact line, which will ensure positive contact with the drive shaft. When the seal element (3) is worn, the gap will stay closed with reduced contact pressure at the contact line. Thus this feature will ensure zero gap at all operating temperatures and will take care of wear. The proposed shaft seal arrangement is easier to install and the gap between the seal elements and the drive shaft will stay closed effectively at all operating temperatures, because of the three-segment configuration with the ability to move the segments radially for closing the gap. The proposed shaft seal design can compensate the effect of wear because of its spring-like construction. This will enhance the effectiveness of the sealing and increase its useful life. The invention described hereinabove is in relation to a non-limiting embodiments and as defined by the accompanying claims. WE CLAIM: 1. A high temperature shaft seal for gas flow divertor in a combined cycle power plant comprising a seal housing (1) having a cover plate (2) k and a iseal element (3) sealing a drive shaft (5) characterized by the said element (3) is having a plurality of segments (4) movable radially inwards for adjustment of the gap caused by wear between the drive shaft (5) and the seal (3) and between any two adjacent segments (4) can be closed, the inner diameter being bent at an angle (A) upto 45° towards gas pressure (6) side from the air/bearing side (7) and the inner diameter of the said seal (3) is kept at smaller than the diameter of the drive shaft (5) so that the edge of the seal element (3) sits against the drive shaftj (5) surface with finite pressure at the contact to ensure zero gap at all operating temperature arjfd pressure. 2. A high temperature shaft seal for gas flow divertor as claimed in Claim 1 wherein the said seal element is made from a sheet of high temperature alloy with high resilience for its spring-like construction. 3. A high temperature shaft seal for gas flow divertor as claimed in Claim 2 the said shaft seal element comprises of at least three segments (4). 4. A high temperature shaft seal for gas flow divertor as claimed in Claim 2 the said segments are movable radially inwards and between the adjacent segments (4). 5. A high temperature shaft seal for gas flow divertor as claimed in Claim 2 the said shaft seal element bent at an angle (A) at the inner diameter and the said angle (A) is at least 5°. 6. A high-temperature shaft seal for gas flow divertor in a combined cycle power plant as herein described and illustrated.

Documents:

2893-del-1998-abstract.pdf

2893-del-1998-claims.pdf

2893-del-1998-correspondence-others.pdf

2893-del-1998-correspondence-po.pdf

2893-del-1998-description (complete).pdf

2893-del-1998-drawings.pdf

2893-del-1998-form-1.pdf

2893-del-1998-form-19.pdf

2893-del-1998-form-2.pdf

2893-del-1998-form-4.pdf

2893-del-1998-gpa.pdf