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Method and Apparatus for High-Efficiency Direct Contact Condensation

National Renewable Energy Laboratory

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PDF Document PublicationWhite Paper (925 KB)

Technology Marketing Summary

Geothermal resources, the steam and water that lie below the earth’s surface, have the potential to supply vast amounts of clean energy. But continuing to produce geothermal power efficiently and economically requires innovative adjustments to the technology used to process it.

In the late 1990s, the pressure of geothermal steam at The Geysers (A geothermal plant in northern California) was falling, reducing the output of its power plants. NREL partnered with Pacific Gas and Electric (PG&E) under a coop­erative research and development agreement to create a solution for boosting production efficiency at the complex.

To generate geothermal energy, power plants at The Geysers capture vapor and water from beneath the earth’s surface, directing it through steam turbines. These turbines drive genera­tors, which produce electricity. Condensation of spent generator steam is a critical part of this power cycle, and in the 1990s, about half of The Geysers’ power plants relied on direct-contact condenser systems to process the steam.

Direct-contact condensers mix cooling water with spent steam in an open chamber, typically relying on a series of perforated plates to provide surface area for conden­sation. The water and condensate mixture is pumped out to cooling towers to be recycled as circulating water, and non-condensable gases—including potential pollut­ants such as hydrogen sulfide—are removed. Standard direct-contact condenser technology have shown to be inefficient, consum­ing too much steam during the removal of non-condensable gases and creating high back pressures that decreased turbine performance.

Description

NREL scientists developed a novel advanced direct-contact condenser (ADCC) for use in geothermal power plant applications. The focus was to develop a system that was more efficient and had lower lifetime costs.

Many plants have surface condenser systems—in which vapor runs around sealed coolant pipes—to prevent the release of hydrogen sulfide into the atmosphere. ADCC systems control hydrogen sulfide emissions as effectively as surface condensers and expend much less energy doing so, driving down overall costs for condenser systems by half. And for new geothermal power plants, ADCC systems cost two-thirds less than traditional direct-contact condenser installations.

In the course of developing the solution, NREL also created a computer model that evalu­ates the thermal performance of possible packing structures for a particular condenser and power plant. In addition to helping geothermal plants determine optimal packing structures, the program models chemical interactions between cooling water and spent steam—an important development for units with high quantities of non-condensable gases.

When combined with intermediate-plate heat exchangers, ADCC technology offers a lower-cost alternative to the surface condenser systems used in fossil fuel power plants. NREL designed an ADCC system with modular heat exchangers that can be cleaned individually, without requiring power plant shutdowns. Sequential clean­ing eliminates condenser downtime that costs the utility industry more than a billion dollars each year, according to Electric Power Research Institute estimates.

Benefits
  • Low cost
  • Power savings
  • Higher efficiency
  • Easier maintenance
Applications and Industries
  • Power generation
  • Condenser technologies
  • Geothermal
Patents and Patent Applications
ID Number
Title and Abstract
Primary Lab
Date
Patent 5,925,291
Patent
5,925,291
Method and apparatus for high-efficiency direct contact condensation
A direct contact condenser having a downward vapor flow chamber and an upward vapor flow chamber, wherein each of the vapor flow chambers includes a plurality of cooling liquid supplying pipes and a vapor-liquid contact medium disposed thereunder to facilitate contact and direct heat exchange between the vapor and cooling liquid. The contact medium includes a plurality of sheets arranged to form vertical interleaved channels or passageways for the vapor and cooling liquid streams. The upward vapor flow chamber also includes a second set of cooling liquid supplying pipes disposed beneath the vapor-liquid contact medium which operate intermittently in response to a pressure differential within the upward vapor flow chamber. The condenser further includes separate wells for collecting condensate and cooling liquid from each of the vapor flow chambers. In alternate embodiments, the condenser includes a cross-current flow chamber and an upward flow chamber, a plurality of upward flow chambers, or a single upward flow chamber. The method of use of the direct contact condenser of this invention includes passing a vapor stream sequentially through the downward and upward vapor flow chambers, where the vapor is condensed as a result of heat exchange with the cooling liquid in the contact medium. The concentration of noncondensable gases in the resulting condensate-liquid mixtures can be minimized by controlling the partial pressure of the vapor, which depends in part upon the geometry of the vapor-liquid contact medium. In another aspect of this invention, the physical and chemical performance of a direct contact condenser can be predicted based on the vapor and coolant compositions, the condensation conditions. and the geometric properties of the contact medium.
National Renewable Energy Laboratory 07/20/1999
Issued
Patent 6,282,497
Patent
6,282,497
Method for analyzing the chemical composition of liquid effluent from a direct contact condenser
A computational modeling method for predicting the chemical, physical, and thermodynamic performance of a condenser using calculations based on equations of physics for heat, momentum and mass transfer and equations of equilibrium thermodynamics to determine steady state profiles of parameters throughout the condenser. The method includes providing a set of input values relating to a condenser including liquid loading, vapor loading, and geometric characteristics of the contact medium in the condenser. The geometric and packing characteristics of the contact medium include the dimensions and orientation of a channel in the contact medium. The method further includes simulating performance of the condenser using the set of input values to determine a related set of output values such as outlet liquid temperature, outlet flow rates, pressures, and the concentration(s) of one or more dissolved noncondensable gas species in the outlet liquid. The method may also include iteratively performing the above computation steps using a plurality of sets of input values and then determining whether each of the resulting output values and performance profiles satisfies acceptance criteria.
National Renewable Energy Laboratory 08/28/2001
Issued
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
ROI 96-34PrototypeAvailable01/06/201401/06/2014

Contact NREL About This Technology

To: Eric Payne<Eric.Payne@nrel.gov>