CONTINUOUS FILTRATION WITH BACKFLUSH CLEARANCE OF ALTERNATE FILTERS

Abstract

Improved steamblow commissioning of a steam plant with continuous filtration of particle laden condensate through dual strainer filters with backflush means operatable in parallel to enable isolation of one and backflushing while the other is backflushed and venting backflushed particles to waste to enable an uninterrupted commissioning process recycling steam with significant particulate burden relived by continuous cycling in alteration through the dual filers and removal of particles to waste with backflush.

Claims

1. In a steamblow commissioning system for steam cycle power plants with boiler, turbine, condenser with interconnection piping means in a closed cycle with high pressure steam routed to the condenser via permanent piping wherein the commissioning includes use of steam blow means to capture particles and routing the steam to the condenser and recycling condensate from the condenser to the boiler, the improvement comprising means for continuous Hushing and removal to waste of particle laden condensate from the condenser and with dual filters operating in alternation with a first filter operating until a selected level of particulate burden is reached, then going out of line while the second filter is engaged in filtering particle laden condensate while the first one is backflushed by an air blast of accumulated air and reversing the roles of the filters repeatedly and without interrupting condenser outflow and transit to the boiler until the commissioning goal of filtration is achieved.

2. Implementing apparatus for the system improvement for steam blow commissioning as set forth in claim I comprising means constructed and arranged for continuous Hushing of particle laden condensate from the condenser and (a) with dual filters of truncated conical basket form pointing upstream in respective housings operating in alternation with a first filter operating until a selected level of particulate burden is reached, (b) then going off line while the second filter is engaged for filtering particle laden condensate while the first one is backflushed by an air blast of accumulated air the reversing the roles of the filters, (c) means for measuring pressure drops between inlet and exit sides of each filter housing to establish a trigger point for backflushing (d) doing such alternating backflush repeatedly and without interrupting Mow of particle laden condensate from the condenser to the multi-filter means or from said filter means to the boiler, the dual filters operating in alternation until the commissioning goal of filtration is achieved.

3. The apparatus of claim 2 wherein the filters comprise mesh strainers of truncated conical form overlaid on expanded metal and within housings having inlet and exit ends with the conical form converging toward the inlet end, each of the filter housings having valving means upstream and downstream of the strainer filters, and further comprising a common air accumulator connected to the downstream portions of each filter housing via valving controllable to selectively blow air through the interior of each strainer forcing particles on the conical strainer though its mesh surface, and further comprising waste lines means with valving connected to inlet ends of the filter housings to enable removal of particles blown from the conical strainer.

4. The apparatus of claim 3 further comprising means for re-charging the air accumulator after each strainer backflush operation.

5. The apparatus of claim 3 further comprising a pressure equalization line with valving to selectively connect the filter housings to a vapor space of the condenser.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIGS. 1 and 2 are schematics of a closed cycle low pressure (LP) steam generating plant including preferred embodiments of the multi-(dual) filter system in simplex (FIG. 1) and parallel (FIG. 2) arrangements; FIG. 3 is an isometric view of the FIG. 1 system with one of its two conduits shown in partial section form; FIGS. 4 is a top view of the FIG. 3 configuration; and FIG. 5 is a side view of the FIG. 3 configuration.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0007] FIGS. 1 and 2 show schematically a preferred embodiment of the condensate filtration portion as a first aspect of the present invention in simplex parallel and duplex arrangements, respectively, placed in the condenser to boiler path of a closed cycle low pressure steam generation plant. The plant itself can operate stand-alone or as a heat recovery supplementary portion of a combined power cycle with one or more primary power cycles based on other sources of energy, (e.g. combustion gas, solar or wind power, geothermal otherwise). In a combined cycle, the steam cycle boiler may be a heat recovery steam generator reheating condensate to steam from primary cycle residual energy use of one of the above energy sources. In normal operation steam is admitted to the turbine T to drive a load (e.g. an electricity generator). Exhaust steam from the turbine is admitted to a condenser COND, which may be (a) of surface cooled form, i.e. with steam cooled on surfaces of liquid cooled pipes (LCPs) therein with circulation of liquid coolant therein or (b) of air cooled condenser types with steam passing through interiors of tubes and cooled by external air. The condenser has a condenser vapor space CVS therein (or in an adjunct condensate tank) and a hotwell HW therein containing liquid condensate that is recirculated to the boiler via one or more condensate pumps CP of permanent plant equipment. In many steam plant systems there is a need for commissioning for initial startups of plants or later startups after offline repairs deal with major particulate and nonparticulate contamination of plant piping and equipment introduction in original manufacturing or refurbishing of the plant. Some commissioning processes include steam blow methods and apparatus to cleanse plant piping and equipment. After an initial trash blow of steam through piping to waste (exhaust), steam is routed the air condenser and condensate is recycled to the boiler. An example of this is in the basic '566 Bloch patent cited above. Filters F are provided in-line between the condenser and condensate pumps that recirculate condensate to the boiler. Per the present invention, filters are preferably provided as fine mesh and truncated conical form strainer baskets, preferably in multiples e.g. two, in parallel so that one can be serviced offline while the other continues flow from the condenser to its condensate pump. See generally FIG. 2 and related text of the '566 patent. As shown in its FIG. 1 herein two conduits lead to entrances of two filters and two filter exits lead to separate condensate pumps CP. As shown in its FIG. 2 herein a common condensate outlet divides to feed filter conduits' inlets depending on open-closed states of inlet valves Vin and outlet valve Vout therein and to pass filtered liquid through a common exit to the condensate pumps, the feed path depending on open-closed status of the inlet and outlet valves. In either of the FIG. 1 or FIG. 2 systems embodiments of the '566 patent the valving preferably puts one or the other of the conduits with its filter in service at a time but in some instances both can be operational in parallel.

[0008] In both the embodiments of FIG. 1 and FIG. 2 herein an air accumulator tank or pipe AA is primed (changed) to a high pressure fill (typically 100-150 psig) by air from a plant air source and when enabled to do so (by opening a valve under manual control or automated response to a rise in differential pressure between inlet and outlet of a filter) admits air to the downstream (exit) side of one or the other of the filters via air lines V, usually just one at a time, to backflush the strainer basket filter to dislodge and drive off particulate material at the filter's upstream (inlet) side. The driving force to dislodge and remove the particles to waste is a turbulent air/liquid mixture that exits the conduit via a waste line W preferably with flow buffered in a backflush containment vessel BCV before release as waste. Differential pressure gauges DP are provided to indicate when an in-service filter is unduly fouled by particle loading leading to a pressure drop and this indication can be used automatically or manually to isolate the parallel conduit of the fouled filter and enable backflushing of it and bring the filter of the other conduit into service to maintain continuity of flow and filtration of flow from condenser to boiler via the condensate pumps. A pressure equalization line PEL with its own valving connects condenser vapor space CVS to one or the other of the conduits (to the one with backflushing in progress) at any given time.

[0009] FIG. 3 shows as an isometric view and FIGS. 4 and 5 show top and side views, with further detail, for either of the FIG. 1 or FIG. 2 embodiments with like reference letters to like components. The filters F (strainer baskets, SB) are contained in strainer basket housing pipe sections SBH inserted into the parallel conduits 12 and 14 connecting a boiler hotwell to condensate suction pumps and then to the boiler or other reheat component. The strainer basket housing pipe sections SBH are larger in diameter than the condenser outlet pipe(s) into which they are inserted to compensate for flow area restrictions of the strainer baskets SB therein. Preferably, the inlet and outlet valves 12 Vin/Vout and 14 Vin/Vout in the two parallel conduits are butterfly valves with arm extensions indicating open (arm in line) or closed (arm at 90 to in-line) status. Differential pressure ports DPP are shown for connecting differential pressure gauges to the conduits upstream/downstream of the filters therein. Waste lines are shown at W with their respective waste line valves Vex leading to a buffering containment vessel (BCV in FIGS. 1 and 2) and a shared check valve (Vck) leads to exhaust.

[0010] The FIG. 3 arrangement is an implementation of FIG. 1 or 2 and partially sectioned at the filter housing SBH of one of the parallel conduits 12 to reveal the strainer basket (mesh strainer) filter SB therein as being of conical form tapering down from outlet end to inlet end (i.e. particles entrained in condensate liquid contact the outside of the tapering cones) and air blown in from the air accumulator blows first to the inside of the tapering cone (downstream side) and through its mesh to dislodge particles and aggregates of particles coating the basket and move them to waste as an air/liquid flow carries the particles away. The waste line valve is then closed and inlet, then outlet valves are closed to allow refill of the SBH section and resumption of filtered flow through without significant air bubbles entrapped therein.

[0011] In FIGS. 1- 5, it is seen that the first conduit 12 and a second conduit 14 have filters F1, F2 and more particularly have strainer basket housings 12SBH and 14SBH therein, respectively, including truncated conical strainer baskets 12SB and 14SB. The arrow A indicates the direction of inlet water (e.g. from the condenser hotwell of the system shown at FIG. 2 of the '566 patent and FIGS. 1 and 2 herein). Waste lines 12W and 14W connect to conduits 12 and 14, respectively. Air accumulator AA is connected to conduits 12 and 14 to selectively, under valve control, access their respective strainer basket housing sections 12SBH and 14SBH.

[0012] Strainer isolation valves (preferably butterfly valves) are provided for conduit 12 at 12Vin and 12Vout, for conduit 14 at 14Vin and 14Vout and for waste lines 12W and 14W in each waste line. The butterfly valves can be manually or power actuated (e.g. pneumatically actuated). When, e.g. the strainer basket 12SB filtering is impeded (fouled) by solids build up (on its water entry side), as indicated by a pressure drop across the strainer measured via differential pressure ports DPP (shown in FIGS. 1, 2, 4 and 5), the valves of conduit 12 can be operated to close to isolate that strainer and valves 14V-in and 14V-out of conduit 12 can be operated to open to let flow run through strainer basket 14SB. High pressure flow of air from intake of air accumulator 12AA opens to blow the strainer 12SB clear creating a mixture of air and turbulent liquid with fouling matter then driven out through waste line 12W via valve Vw and an exhaust valve i.e. a check valve Vck. The waste lines and lines from the accumulator means to the strainer basket housings have diameters of a significant size in relation to strainer basket housing diameters, preferably over 20% and in some usages significantly higher. The backflushing and related valve operations can be accomplished in seconds.

[0013] An air inlet port AIP is provided to recharge the exhausted air accumulator after each backflush usage and a water inlet port WIP to recharge each conduit with water after its backflushing operation is complete. A level-sighting glass is provided for each conduit.

[0014] Differential pressure gauges (DP) (shown in FIGS. 1, 2) are applied to conduits 12 and 14 via pressure ports indicated at DPP. When the differential pressure gauge for a conduit shows a change in pressure drop on the strainer in that conduit above a set point, it signals the isolation valves for that conduit to close and its waste line valve to open and for the applicable air entry line from the air accumulator AA to open after the strainer basket filter is isolated. The ports are threaded and installed both upstream and downstream of each strainer basket in order to connect differential pressure gauges therebetween. Differential pressure across the strainer basket must be monitored during operation. As the strainer fouls, differential pressure across the strainer increases, which if unresolved, leads to excessive differential pressure that can result in pump cavitation or structural failure of the strainer basket. Sight glasses are attached to the conduits in order to provide a visual indication to the operator that a flush was successful (water level decreases out of sight glass range) and when refilling of the clean strainer is complete the water level increases to visibility in a sight glass range.

[0015] The system is preferably self-regulating with switched usage/backflushing between conduits 12 and 14 determined by fouling of its respective strainer basket rather than fixed time intervals of switching but in some systems, a series of fixed time intervals can be employed. The monitoring and valve operation and backflush can be manually controlled or automated.

[0016] Water inlet lines WIL are provided on edges of backflushed conduits and air inlet lines AIL with air inlet ports AIP for recharging the air accumulator under ball valve control (BV). The air lines include a connection to a vapor space in a water source tank (not shown) that feeds the water line.

[0017] The open area totals for a basket (SB) of each mesh strainer, add up, preferably, to 150% or more flow area of the conduit 12 or 14 in which it is contained.

[0018] The strainer mesh should have hole sizes equal to or smaller than the hole sizes on the boiler feed pump suction strainers. This insures that contaminants won't be passed through the condensate pumps which could then foul the boiler feed pump strainers. Typical power plant jobs use a mesh size of 80-100 mesh. The strainer should point upstream (the truncated point of the cone towards the condenser). The strainer mesh must be on the outside of the strainer cone. The strainer should be manufactured with the cone made from perforated plate, the mesh outside the cone, and a second very coarse retaining mesh to restrain the fine mesh during flushing. Under no circumstances should fine mesh be attached to the inside of the cone, since mesh failure could result in catastrophic pump damage in this configuration.

[0019] The vent line should be about 2 for most applications to allow for rapid refilling of the strainers after flushing. The vent line must be routed so that it is downhill from the condenser vapor space to the strainer, with no pockets. This configuration allows the line to drain back to the strainer, without forming liquid seals which would defeat the function of the vent line. The vent line should have a glass-type flow indicator so the operator is aware when the strainer is refilled with water. The flow area of the air connection to the receiver and the waste line should be greater than 10% of the flow area of the strainer housing. This will insure adequate flushing velocities. The waste line should be as short as practical to avoid excessive line losses. The waste line should be routed to a sump to contain the splash when backflushing. If a suitable sump is not available, then the line can be routed to a muzzler type froth slug catcher.

[0020] The waste line will be subject to high dynamic loads. It must be adequately supported to resist these loads. The design of the supports also must not impose excessive pipe stresses on the condensate pump suctions, particularly in thermal cases when the lines heat up. The design of the waste piping should be reviewed by a competent stress analyst.

[0021] The valves to control the strainer can be manually actuated or automatic. Air and waste valves will typically be automated if they are greater than 6. Automated air valves should have an interlock in the control panel that prevents opening the air valve unless the strainer isolation valves are closed. This is to prevent the accidental discharge of air into the suction of an operating pump.

[0022] The air tank has a secondary block valve which should be closed except when the backflush system is in active use. This secondary block helps to avoid air leakage into the pump suctions. The volume of the air tank should be at least 50% of the volume of the suction piping/strainer assembly which it will be evacuating. The nozzle size of the receiver should provide a flow area greater than 10% of the strainer housing flow area. The flow nozzle can be combined with an inspection manway through the use of an adapter piece. Flexible hoses should be avoided in the air side of the system. If flexible hoses are used, the safety protocols developed for froth flushing should be used.

[0023] A valve must exist between the air receiver and the hose. A length of hard piping with a length 1.5 times the flex hose should be installed downstream of the valve, and before the flexible hose. The isolation valve should be closed except when the system is in active use, i.e. a pressurized flexible hose should not be left unattended for extended periods of time.

[0024] Each strainer has a differential pressure gauge across it which will indicate strainer fouling. Suction strainers are structurally designed for greater than 10 psi, preferably equal to or greater than 20 psi. These are preferred limits but some systems may be designed for lower or higher ranges. Upper limits depend on practical cost, conductivity and sizing considerations of thickness, porosity and weight. Strainer differential pressure are maintained below the applicable lower limit to avoid a structural failure of the strainer assembly. Net pressure suction head (NPSH) must also be maintained on the suction side of the condensate pumps at all times to prevent cavitation of the pumps.

[0025] The strainer system should be equipped with tapping points so the permanent plant differential pressure transmitters can be connected. All automatically controlled pumps are set to trip for high differential pressure and low condensate pump NPSH should be utilized. Auto start logic should be disabled since the pump suctions will not be in their permanent configuration.

[0026] The system should be equipped with a small pressure sensing valve (PSV) between the downstream isolation valve and the pump. This pressure sensitive valve prevents over-pressurization of the strainer assembly and the expansion joint in the event of leakage of the discharge check valve in standing-by pump. If a permanent PSV with this function exists, it should be temporarily relocated to the temporary piping.

[0027] The components of the strainer system should be standardized and flanged to the greatest degree possible to facilitate reuse of the components on multiple projects. This dual strainer feature with rapid cyclic backflushing can be used in systems with surface condensers and air cooled condensers. But air cooled condensers used are preferably pre-rinsed in advance of in-line usage in commissioning to prevent an excessive load of contamination from overwhelming the filter system.

[0028] The above described system is one that is temporarily installed for commissioning and used for managing liquid flows with high loading of particulate contaminants at one or more stages of commissioning operation, enabling switching of first and second conduits/strainer baskets without stoppage of flow and avoidance of conduit section removal, manual cleaning steps and shut down dangers.

[0029] A further attribute of the present invention is that it is capable of functioning in a low or negative pressure applications with high burden of particulate matter in flowing liquid and less costly compared to known self-cleaning strainer assemblies used in many industrial processes, including low suction head operations, such as are shown at http://www.tekleen.com. However, in the above described significant steam plant usage of the present invention, simple strainers can be used on the condensate pumps as backups to filtration provided continuously and reliably by the present invention.

[0030] It will now be apparent to those skilled in the art that other embodiments, improvements, details, and uses can be made consistent with the letter and spirit of the foregoing disclosure and within the scope of this patent, which is limited only by the following claims, construed in accordance with the patent law, including the doctrine of equivalents.