Air-Cooled Steam Condenser with Improved Second Stage Condenser

The present invention relates to large scale field erected air cooled industrial steam condensers.

Due to the decreasing availability and rising cost of cooling water, direct air-cooled steam condensers (ACC) are used instead of indirect evaporative cooling towers to dissipate heat into the environment in power plants that incorporate steam turbines.

In a direct ACC, the steam exiting a steam turbine is fed via a turbine exhaust duct and steam duct manifolds to a set of primary condenser tubes (first stage condenser). Residual steam leaving the primary condenser tubes is then condensed in a set of secondary condenser tubes (second stage condenser, dephlegmator or reflux condenser). Second stage, or secondary, condenser tubes minimize backflow, which is flow from the outlet manifold of the primary tubes into the intended outlet of a fraction of the primary tubes. Backflow is caused by a pressure variation among the primary tubes. Tubes with higher outlet pressures raise the outlet manifold to a pressure greater than that of tubes with lower outlet pressures. This causes vapor to flow from the outlet manifold into those tubes with lower outlet pressures. When backflow occurs in a primary tube, the tube effectively has two vapor inlets and no vapor outlet path for the non-condensable gases, which accumulate into a pocket or dead zone. The formation of dead zones in condenser tubes reduces the capacity of the ACC to condense steam and may subject the condensate in the tubes to freeze.

Located downstream of the primary condenser tubes outlet manifold in the steam path, the secondary condenser tubes enable additional vapor flow through the primary condenser tubes, which increases the pressure drop through the primary tubes and reduces the outlet manifold pressure. Greater pressure variations among the primary tubes are required to cause backflow when the outlet manifold pressure is reduced. Therefore, a two-stage condenser is more resistant to pressure variations and the formation of dead zones. The secondary condenser tubes collect non-condensable gases from the primary tubes to be separated out and typically vented to atmosphere through an air-removal system consisting in vacuum pumps or steam jet air ejectors, or both.

An ACC is typically arranged in rows or streets of modules or cells, each in line with the steam distribution manifolds. Several rows or streets may be arranged adjacent one-another to form a rectangular array of cells or modules. Each row or street incorporates primary condenser tubes and secondary condenser tubes, either in separate cells or modules, or interspersed among them. HEI Standard states in section 2.29 that “the second stage cell collects the remaining steam and the non-condensables and is connected with the air-removal system at the top and the condensate header at the bottom. It is also referred to as a Dephlegmator, Secondary or Reflux cell.”

According to K Wilber and K Zammit (EPRI's ACC Guideline), “The total number of cells or modules is the sum of the Primary and Secondary Modules. The Primary Modules are responsible for the majority of the heat transfer and condensing, while the Secondary Cells are responsible for residual heat transfer and non-condensable collection and evacuation. ( . . . ) The number of Primary Modules is typically about 80 percent of the total number of modules. ( . . . ) The number of Secondary Modules is typically about 20 percent of the total number of modules and there is typically one module per row (or street).”

Owen (Stellenbosch University, Air-cooled steam condensers) investigated “the steam-side operation of a practical air-cooled steam condenser using a combination of CFD, numerical, analytical and experimental methods,” while directing particular attention “towards the vapor flow distribution in the primary condensers and dephlemator performance.” Owen demonstrated that “The vapor flow in the primary condensers is shown to exhibit a non-uniform distribution amongst the heat exchanger tubes. ( . . . ) The non-uniform flow distribution places an additional demand on dephlegmator performance, over and above the demands of row effects in the case of multi-row primary condenser bundles.” Owen focused his investigation on the effects of multiple-row condenser bundles and the influence of transverse variations in tube inlet loss coefficients. Owen further concluded that “The use of single-row primary condenser bundles holds the greatest potential for reducing the demands on the dephlegmator. By eliminating the row effect in the primary condensers, dephlegmator loading can be reduced by up to 70%. The resultant large margin of safety to cope with non-ideal operation is highly desirable in light of the well documented negative effects of wind on fan performance and recirculation at large ACCs.”

Our own experiments have demonstrated that, even with single-row condenser tube bundles, non-uniform distribution of vapor flow in the primary condenser tubes and resulting pressure variations occur as the result of variations of face air velocity between the heat exchanger tubes and the effect of wind gusts over the face of the heat exchangers, among the external parameters that affect the condensing capacity of the ACC. These non-ideal operating conditions place a burden on the secondary condenser tubes, which would lead the person of ordinary skill in the art to improve it by increasing the proportion of secondary condenser tubes. However, we have discovered that as the proportion of secondary tubes increases, the proportion of primary tubes decreases leading to a corresponding increase in the steam velocity and steam side pressure drop in the primary tubes. The increase in pressure drop and associated reduction in condensing temperature reduces the thermal performance, or condensing capacity of the ACC, particularly at low pressure operating conditions. It is therefore of interest to reduce the overall dimensions and cost of the ACC, to maximize the extent of the primary condenser tubes, and to minimize the extent of the secondary condenser tubes.

The invention presented herein is a new and improved design for large scale field-erected air cooled industrial steam condensers for power plants and the like which provides significant improvements and advantages over the ACCs of the prior art. The innovation in this invention is that each primary condenser tube has a cap or plate at its outlet end having a flow orifice, so that each orifice provides a steam-side pressure loss which reduces the outlet manifold pressure and prevents backflow among the primary tubes. The average flowrate through the orifice is determined by the proportion of secondary tubes in the design. The size of the orifice and the proportion of secondary tubes are selected to reduce the outlet manifold pressure to a desired target in order to regulate and balance the vapor flow across the primary condenser tubes, to eliminate the risk of backflow and to prevent the formation of dead zones at the top of the primary condenser tubes.

The primary tube outlet orifices may have an area of less than or equal to one half of the cross-sectional area of the tube itself.

The incorporation of orifices in the outlet end of each primary condenser tube allows to greatly reduce the amount of secondary condenser tubes while reducing the outlet header pressure sufficiently to minimize backflow, sweep non-condensable gases and prevent the formation of dead zones. The secondary condenser tubes allow non-condensable gases to be separated out and vented to atmosphere through the air-removal system.

According to one embodiment of the present invention, heat exchanger panels are constructed with an integral secondary condenser section positioned essentially in the center of the heat exchanger panel, flanked by primary condenser sections which may or may not be identical to one-another. A bottom bonnet runs along the bottom length of the heat exchanger panel, connected to the bottom side of the bottom tube sheet, for delivering steam to the bottom end of the primary condenser tubes. In this arrangement, the first stage of condensing occurs in counter-current operation. The tops of the tubes are connected to a top tube sheet, which in turn is connected on its top side to a top bonnet. See e.g., U.S. Pat. No. 10,982,904, the disclosure of which is incorporated herein in its entirety. According to the present invention, each primary condenser tube incorporates a cap or plate at its top/outlet end, the cap or plate having a narrowed flow orifice. The orifices may be rectangular, round elliptical or round and may have an area of about 50% or less of the cross-sectional area of the tube itself. Uncondensed steam and non-condensables flow into the top bonnet from the primary condenser tubes through the orifices and flow toward the center of the heat exchanger panel where they enter the top of the secondary condenser section tubes. In this arrangement the second stage of condensing occurs in co-current operation. Non-condensables and condensate flow out the bottom of the secondary tubes into an internal secondary chamber located inside the bottom bonnet. Non-condensables and condensate are drawn from the bottom bonnet secondary chamber via an outlet nozzle, non-condensable gases are separated out and sent to the air-removal system, and condensate is drawn off and sent to join the water collected from the primary condenser sections. The fraction of primary condenser tubes is as much as or greater than 90% of the total heat exchanger section of the ACC and the fraction of secondary condenser tubes is as little as or less than 10% of the total heat exchanger section of the ACC.

Features in the attached drawings are numbered with the following reference numerals:

As outlined in the Summary of the Invention, a central innovation of the present invention is a primary condenser tube for an ACC having primary tube outlet cap/platewith an outlet orificeas shown in. The orifices can have any shape, including round, rectangular, oval and elliptical. Each tube may have an outlet cap/plate with only a single orifice, or each tube's outlet cap/plate may have more than one orifice. The total area of all outlet orificesfor one tube is preferably 50% or less of the cross-sectional area of the tube. According to preferred embodiments, the total area of the one or more outlet orifices for a single tube is 5% to 50% of the cross-sectional area of tube. According to more preferred embodiments, the total area of the one or more outlet orifices for a single tube is 10% to 40% of the cross-sectional area of tube. According to even more preferred embodiments, the total area of the one or more outlet orifices for a single tube is 20%-30% of the cross-sectional area of the tube. The proportion of primary condenser tubes to secondary condenser tubes in a cell/module, in a row or street of cells/modules, or across the entire ACC is preferably 90:10, but may range from 85:15 to 95:5. As noted above, the size of the primary tube outlet orificesand the proportion of secondary tubes may be selected to reduce outlet manifold pressure to a desired target in order to regulate and balance the vapor flow across the primary condenser tubes, thereby reducing or eliminating the risk of backflow and the formation of dead zones at the top of the primary condenser tubes.

The features of the invention may be used in conjunction with ACCs of any configuration, but are most preferably in conjunction with an ACC according to the various configurations shown in. Referring to, the heat exchanger panelincludes two primary condenser sectionsflanking an integrated and centrally located secondary condenser section. Each heat exchanger panelconsists of a plurality of separate condenser bundles, with a first subset of condenser bundlesmaking up the centrally located secondary section, and a second subset of different condenser bundlesmaking up each flanking primary section. The dimensions and constructions of the tubesof the primary and secondary sections are preferably identical with the exception of the outlet orifices at the top of the tubes in the primary section. At their top, all of the tubesof both the primary and secondary sections,are joined to a top tube sheet, on which sits a hollow top bonnetwhich runs the length of the top of the heat exchanger panel. The bottom of all of the tubesof the primary and secondary sections,are connected to a bottom tube sheet, which forms the top of a bottom bonnet. The bottom bonnetlikewise runs the length of the heat exchanger panel. The bottom bonnetis in direct fluid communication with the tubesof the primary sectionbut not with the tubes of the secondary section. The bottom bonnetis fitted at the center point of its length with a single steam inlet/condensate outletwhich receives all the steam for the heat exchanger paneland which serves as the outlet for condensate collected from the primary sections. The bottom of the bottom bonnetis preferably angled downward at an angle of between 1° and 5°, preferably about 3° with respect to the horizontal from both ends of the bonnettoward the steam inlet/condensate outletat the middle of the heat exchanger panel. According to a preferred embodiment and referring to, the bottom bonnetmay include a shield plateto partition condensate flow from the steam flow. The shieldmay have perforationsand/or have a scalloped edgeor have other openings or configuration to allow condensate falling on top of the shieldto enter the space beneath the shield and to flow beneath the shield toward the inlet/outlet. When viewed from the end of the bottom bonnet, the shield plateis secured at a near-horizontal angle (between horizontal and 12° from horizontal in the crosswise direction) so as to maximize the cross-section provided by the bottom bonnetto the flow of steam. The shield platemay be flat as shown inor bended as shown in. The top tube sheetand bottom tube sheetmay be fitted with lifting/support anglesfor lifting and/or supporting the heat exchangers.

An internal secondary chamber, or secondary bottom bonnet, is fitted inside the bottom bonnetin direct fluid connection with only the tubesof the secondary sectionand extends the length of the secondary section, but preferably not beyond. This secondary bottom bonnetis fitted with a nozzleto withdraw non-condensables and condensate.

The steam inlet/condensate outletfor the heat exchanger paneland the steam inlet/condensate outletsfor all of the heat exchanger panels in the same ACC cell/moduleare connected to a steam distribution manifoldlocated beneath the heat exchanger panelsand which runs perpendicular to the longitudinal axis of the heat exchanger panelsat their midpoint See, e.g.,. In this embodiment, the steam distribution manifoldextends across the width of the cell/moduleand continues to adjacent cell/modules. Where the top surface of the steam distribution manifold (SDM)passes below the center point of each heat exchanger panel, the steam distribution manifoldis fitted with a Y-shaped nozzlewhich connects to the steam inlet/condensate outletsat the bottom of each adjacent pair of heat exchanger panels(See, e.g.,).

According to this construction, each cellof the ACC receives steam from a steam distribution manifoldlocated directly beneath the center point of each heat exchanger panel, and the steam distribution manifoldfeeds steam to each of the heat exchanger panelsin a cellvia a single steam inlet/condensate outlet.

Therefore, the steam from an industrial process travels along the turbine exhaust ductat or near ground level, or at any elevation(s) suited to the site layout. When the steam ductapproaches the ACC of the invention, it splits into a plurality of sub-ducts (steam distribution manifolds), one for each street (row of cells)of the ACC (See, e.g.,). Each steam distribution manifoldtravels beneath its respective street of cells. The steam distribution manifoldmay be suspended from the frameof the condenser module, supported in the frame of understructure moduleor supported from below by separate structure. The steam distribution manifolddelivers steam through a plurality of Y-shaped nozzlesto the pair of bonnet inlets/outletsof each adjacent pair of heat exchanger panels,. The steam travels along the bottom bonnetand up through the tubesof the primary sections, condensing as air passes across the finned tubesof the primary condenser sections. The condensed water travels down the same tubesof the primary sectioncounter-current to the steam, collects in the bottom bonnetand eventually drains back through the steam distribution manifoldand turbine exhaust ductto a condensate collection tank (see, e.g.,). According to a preferred embodiment, the connection between the bottom bonnetand the steam distribution manifoldmay be fitted with a deflector shieldto separate the draining/falling condensate from the incoming steam.

The uncondensed steam and non-condensables are collected in the top bonnetand are drawn to the center of the heat exchanger panelwhere they travel down the tubesof the secondary sectionco-current with the condensate formed therein. Non-condensables are drawn into the secondary bottom bonnetlocated inside the bottom bonnetand out through an outlet nozzle. Additional condensed water formed in the secondary sectioncollects in the secondary bottom bonnetand travels through the outlet nozzleas well and then travels through condensate pipingto the steam distribution manifoldto join the water collected from the primary condenser sections.

According to another feature of the invention, the heat exchanger panelsare suspended from frameworkof the condenser moduleby a plurality of flexible hangerswhich allow for expansion and contraction of the heat exchanger panelsbased on heat load and weather.shows how the hangersare connected to the frameof the condenser module.

The heat exchange panelsmay each be independently loaded into and supported in heat exchange module framework. The heat exchange panelsmay be supported in the heat exchange module frameworkaccording to any of a variety of configurations.show the heat exchange panelsindependently supported in the heat exchange module frameworkwith adjacent heat exchange panelsinclined relative to vertical in opposite directions in V-shaped pairs.

According to one embodiment of the invention, shown in, the steam distribution manifoldsmay be connected directly to an elevated turbine steam ductand each steam distribution manifoldruns the beneath the center points of the heat exchange panels of a plurality of heat exchange modules along the length of a street/rowof condenser cells. The steam distribution manifoldsmay be suspended from the heat exchange module frame as discussed previously or may be supported by other portions of the ACC frame, or may be supported from below by a separate structure.

According to a further alternate embodiment of the invention, shown in, the plurality of steam distribution manifolds (SDM)may be connected to a ground level turbine exhaust duct(GLTED)via end risers.

According to preferred embodiments of the invention, the ACCs of the invention are constructed in a modular fashion. According to various embodiments, understructure, condenser modulesand plenum sectionsmay be assembled separately and simultaneously on the ground. Once the condenser moduleis assembled it may be lifted and placed on top of the corresponding completed understructure(See, e.g.,).

The plenum sectionfor each ACC module, including the plenum section frame, fan deck supported on the plenum section frame, fan(s) and fan shroud(s), may be assembled at ground level with a single large fan, as shown, e.g., in, or it may be assembled (also at ground level) with a plurality of elongated fan deck plates, each supporting a plurality of smaller fansin a row, as shown in.

While the assembly described herein is described as being performed at grade, the assembly of the various modules may be performed at their final position if planning and construction schemes allow.

Every feature and alternative embodiment herein is intended and contemplated to work with and be used in combination of every other feature and embodiment described herein with the exception of embodiments with which it is incompatible. That is, each heat exchange module arrangement described herein, and each heat exchange panel arrangement described herein, and each tube type and each fin type described herein, each steam manifold arrangement described herein, and each fan arrangement, is intended to be used in various ACC assemblies with every combination of embodiments with which they are compatible, and the inventors do not consider their inventions to be limited to the exemplary combinations of embodiments that are reflected in the specification and figures for purpose of exposition.