MXPA96001654A - Method and apparatus for generating electric energy apparatus of geothermal fluid containing a relatively high concentration of non-condensate gases - Google Patents

Abstract

The present invention relates to a method for generating energy from geothermal steam, which contains more than about 5% non-condensable gases, the method is characterized in that it comprises: a) expanding the geothermal steam to produce energy and from the discharge steam it is extracted at a pressure above atmospheric pressure, b) indirectly contacting the discharge steam with clean water to condense the discharge vapor at a pressure above atmospheric pressure to produce a geothermal vapor condensate and to vaporize clean water to produce clean steam, c) extract from the heat exchanger, non-condensable gases contained in the geothermal vapor, d) expand the clean steam to produce energy and clean discharge steam, e) condense the clean discharge steam under pressure subatmospheric to produce a clean condensate, and f) returning the clean condensate to the lime exchanger

Description

: METHOD AND APPARATUS FOR GENERATING ELECTRICAL ENERGY FROM OF GEOTHERMAL FLUID CONTAINING A CONCENTRATION RELATIVELY HIGH NON-CONDENSABLE GASES.

FIELD OF THE INVENTION This invention relates to a method and apparatus for generating electrical power from geothermal fluid containing a high concentration (i.e., greater than about 5%) of non-condensable gases (CNG).

BACKGROUND OF THE INVENTION Recently, geothermal sources suitable for the production of electrical energy have been discovered, where the geothermal fluid contains high levels of non-condensable gases (CNG). The non-condensable gases (CNG), particularly at high levels, adversely affect the thermal efficiency of the heat exchangers by which the heat present in the geothermal fluid is transferred to another fluid such as air or water, which is found, for example, in a condenser, or to a working fluid such as water or an organic fluid (eg, isopentane) that is in a vaporizer. When a condenser is involved, the presence of non-condensable gases on the side of the geothermal fluid makes it difficult to obtain very low condensing temperatures on the water side of the condenser, thus limiting the power level of a steam turbine. As a result, it is conventional to extract the non-condensable gases from the condenser associated with a steam turbine operating with geothermal vapor containing the gases, and inject the extracted gases, if preferred or if necessary, into the earth, using a well of reinjection This technique reduces the size of the exchangers, and hence the capital cost of an electric power plant, resulting in a smaller and more efficient plant. In any case where the steam turbine operates with a condenser whose temperature is such that the pressure of the condenser is considerably below the atmospheric pressure, to maximize the pressure ratio through the turbine and thus maximize the work produced, the Non-condensable gases extracted from the condenser will also be below atmospheric pressure. To extract these gases from the condenser, these must be pressurized; and when the level of non-condensable gases in the geothermal vapor is high, a considerable loss of energy produced by the power plant is incurred due to the work required to pressurize the large quantities of these gases.

Quite apart from the specific problems associated, and discussed above, with a geothermal installation that produces steam with a high level of non-condensable gases, is the aging of the geothermal field. That aging usually results in volumetric flow variations, accompanied by decreases in the temperature and pressure of the geometric fluid. A geothermal power plant built for a set of design conditions becomes less efficient as the parameters of the geothermal fluid move from the design point, and energy production decays over time. The conventional solution to this problem is to drill additional production wells and try to maintain design conditions. Although this approach is often feasible, it is sometimes impractical, in some fields, and it is very difficult to predict, during the initial development of a field, if the aging process of the field can be fixed. In these cases, an undesirable element of risk is associated with the large capital investments necessary to develop the geothermal fields. It is therefore an object of the present invention to provide a new and improved method, and an apparatus for generating electrical energy from geothermal fluid containing high levels of non-condensable gases, which reduce, or substantially exceed, the outlined problems. previously.

DESCRIPTION OF THE INVENTION An energy plant in accordance with the present invention, which operates with geothermal steam containing more than about 5% non-condensable gases, comprises a steam turbine that uses the initial steam from the well (hereinafter referred to as the primary steam turbine) which is a turbine that is used to produce exhaust vapor at a pressure above atmospheric pressure, and an indirect contact heat exchanger, containing clean water to condense the exhaust vapor at a pressure above atmospheric pressure, to produce a condensed geothermal steam, and to vaporize clean water accordingly to produce clean steam. The non-condensable gases contained in the geothermal vapor are extracted from the interca-heat absorber. Both these gases and the geothermal vapor are at a pressure above atmospheric pressure, and consequently, without additional pressurization, both can be injected directly to the earth, or can be vented to the atmosphere, or can be treated with others. media.

The clean steam produced by the heat exchanger is applied to another steam turbine (hereinafter called secondary steam turbine) which expands the clean steam to produce clean electrical energy and exhaust steam. A condenser that operates at a pressure below atmospheric condenses the clean steam to produce clean condensate that is returned to the heat exchanger by a pump to complete the cycle. The supply of a primary steam turbine allows the initial conversion of only a fraction (eg, approximately 25%) of the total available energy in the geothermal steam and achieves a dual purpose. First, the non-condensable gases can be extracted at a pressure above atmospheric in such a way that the extraction can occur without the expenditure of energy for the pressurization of these gases. Second, the secondary steam or condensation turbine can be designed as efficiently as possible to produce, for a long period of time, a large part (for example, 75%) of the total available energy in the initial geothermal steam obtained of the field. Because the primary steam turbine can be modified in the field, relatively easy, altering its stages to accommodate variations in steam conditions, the condensing turbine can be isolated from variations in flow and conditions. in the geothermal steam. In addition, when using in the secondary steam turbine, clean steam that does not contain non-condensable gases, the energy required to maintain the subatmospheric pressure in the condenser of this turbine is substantially reduced, and from a practical point of view it is negligible.

BRIEF DESCRIPTION OF THE DRAWINGS With reference to the single figure of the attached drawings, there is described, by way of example, an energy plant in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawing, the reference number 10 designates an energy plant in accordance with the present invention. The power plant 10 includes a medium in the form of a separator 12 responsive to the geothermal fluid derived from the production well 14 to produce geothermal steam. However, it will be understood that the present invention is applicable to power plants, even if a separator is not used. The separator 12 separates the geothermal fluid into a vapor stream 16 containing geothermal vapor and non-condensable gases, and a liquid stream 18 containing geothermal brine. The power plant 10 also includes a primary steam turbine 20 coupled to the generator 22, to perform the expansion of the geothermal steam and produce electrical energy and from which discharge steam is extracted, on line 24 at a pressure above the atmospheric pressure. The vapor from the expansion is applied to an indirect contact heat exchanger 26, which contains clean water and is condensed to produce geothermal vapor condensate, which exits line 28 as the clean water vaporizes to produce steam clean on line 30 at a pressure greater than atmospheric pressure. The pressure ratio through the turbine 20 is preferably 2: 1 with the result that under normal circumstances, the pressure on the steam side 27 of the heat exchanger 26 will be above the atmospheric pressure. For example, if the geothermal steam in the steam stream 16 has a temperature of about 182 ° C and a pressure of about 10.5 barA, the turbine 20 is effective to produce discharge steam at a temperature of about 155 ° C and a pressure of approximately 5.5 barA. The pressure of the clean steam, in that case, will be approximately 3.3 barA.

The line 32 connected to the side of the geothermal steam, of the heat exchanger 26, constitutes a means for extracting the non-condensable gases contained in the discharge vapor of the heat exchanger. The pressure of the steam side in the heat exchanger, preferably it is significantly above atmospheric pressure, for example, approximately 3.5 barA, and it is sufficient to effect by itself the extraction of the non-condensable gases as well as the geothermal vapor condensate from the heat exchanger. If preferred, the non-condensable gases and the geothermal steam condensate can be injected without further pressurization into the reinjection well 34. The plant 10 further includes a secondary steam turbine 36, coupled to the generator 37 to perform the expansion of the clean steam. of line 30 and produce electric power and clean discharge steam that leaves the turbine by the discharge line 38. The condenser 4, which can operate, either with water or cooling air, condenses the clean discharge steam for produce the clean condensate. The condenser 4 operates at below atmospheric pressure allowing the turbine 36 to extract a maximum amount of clean steam energy. As an example, the pressure in the condenser 40 may be approximately 0.08 barA, and the temperature may be approximately 41.5 C. Finally, the cycle pump 42 returns the clean condensate to the water side 25, of the heat exchanger 26, to complete the loop of clean water. Preferably, the secondary steam turbine will produce approximately 75% of the total energy produced by the power plant, and will be designed based on the conditions of the steam produced by the heat exchanger 26. Over time, as the geothermal field gets older, the geo-thermal vapor condition changes; and the changes would normally be reflected in changes in steam conditions on line 30. To isolate turbine 36 from changes in geothermal vapor conditions, two techniques are used in the present invention. First, derivation line 44 is provided; and second, the primary steam turbine 20 is constructed in a manner that facilitates its modification. The bypass line 44, which bypasses the turbine 20, includes the control valve 46 to selectively apply the geothermal vapor from line 16 directly to the heat exchanger 26. When the valve 46 is fully open, the turbine 20 it can be completely deprived of geothermal steam, allowing this turbine to be disconnected, for example, to maintain it, etc., without interrupting the operation of the power plant, whose total energy will be reduced only by the contribution of the primary steam turbine , the output of which, according to the invention, is relatively small. Further, if necessary, the bypass 44 can be used in parallel with the primary steam turbine 20 during start-up or shutdown, for example, to supply a portion of the geothermal fluid directly to the steam side of the exchanger 26. The construction of the Primary steam turbine 20 also contributes to the isolation of the secondary steam turbine 36, from variations in the conditions of the geothermal steam in the line 16. Preferably, the turbine 20 is a multi-stage turbine which is shown in the drawings having a stage or stages 20A of high pressure and a stage or steps 20B of low pressure, interconnected by the shaft or shaft 21 supported by a pair of bearings.

The generator 22. is interposed or placed between steps 20A and 20B; and is mounted directly on the shaft 21. The housings 23A and 23B enclose the respective high and low pressure stages. Preferably, the speed of rotation of the turbine stages is the same as the speed of rotation of the electric generator and preferably, it is relatively low at approximately 1500 RPM or 1800 RPM depending on the frequency of the electrical load to which the generator feeds. . Alternatively, under appropriate situations, the stages 20A and 20B of the primary steam turbine 20 can be parallel stages in which the geothermal steam of the line 16 is applied in parallel to the stages 20A and 20B. The turbine, which preferably has no more than about two or three high pressure stages, and no more than about two or three low pressure stages, is designed in such a way that the stages can be altered or replaced relatively easily and quickly. , in such a way that it is possible to make efficient use of geo-thermal steam when its conditions change as a result of the aging of the geothermal field. In this manner, the efficiency of the primary steam turbine can be maintained in the presence of changing inlet conditions, and the nature of the steam discharged by this turbine can be such that it maintains clean steam conditions of line 30, substantially constant. , in the presence of the changing conditions of geothermal steam. Finally, the geothermal brine of the line 18 produced by the separator 12 can be deposited in the reinjection well 34, either separately or after being combined with the non-condensable gases of the heat exchanger 26 as shown in the drawing . The advantages and improved results described by the method and apparatus of the present invention are apparent from the foregoing description of the preferred embodiment of the invention. Various changes and modifications can be made without departing from the spirit and scope of the invention, as described in the appended claims.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, the content of the following is claimed as property:

Claims (18)

1. An electric power plant operating with geothermal fluid containing more than about 5% non-condensable gases, the electric power plant is characterized in that it comprises: a) a means to produce geothermal steam from the geothermal fluid; b) a primary steam turbine to perform the expansion of geothermal steam and produce electrical energy, and from which it extracts discharge or exhaust steam, at a pressure above atmospheric pressure; c) an in-direct contact heat exchanger, containing clean water to condense the discharge vapor and produce geothermal vapor condensate, and to vaporize the clean water to produce clean steam; d) means for extracting non-condensable gases contained in the discharge vapor from the heat exchanger; e) a secondary steam turbine to perform the expansion of clean steam to produce electrical energy and from which exhaust or exhaust vapor is extracted; f) a condenser operating at a pressure below atmospheric pressure to condense clean steam and produce clean condensate; and g) a pump to return the clean condensate to the heat exchanger.

2. An electric power plant according to claim 1, characterized in that it includes a means for transporting non-condensable gases, extracted from the heat exchanger, to a reinjection well.

3. An electric power plant according to claim 1, wherein the ratio of energy produced by the primary steam turbine to the electric power produced by the secondary steam turbine is approximately 4: 1.

4. An electric power plant according to claim 1, characterized in that it includes a bypass line that derives the primary steam turbine, the bypass line includes an open / close valve to selectively apply the geothermal steam directly to the heat exchanger of direct contact, thus deriving the primary steam turbine.

5. An electric power plant according to claim 1, characterized in that it includes a separator sensitive to the geothermal fluid, to separate it in a steam stream containing geothermal vapor and non-condensable gases, and a stream of liquid containing geothermal brine.

6. An electric power plant according to claim 5, characterized in that the geothermal brine is discarded to a reinjection well.

7. An electric power plant according to claim 1, characterized in that the pressure ratio through the secondary steam turbine is greater than the pressure ratio through the primary steam turbine.

8. An electric power plant according to claim 7, characterized in that the pressure ratio through the primary steam turbine is about 2: 1.

9. A method for generating electrical energy from geothermal steam containing more than about 5% of non-condensable gases, the method is characterized in that it comprises: a) carrying out the expansion of geothermal steam to produce electrical energy and from which discharge steam is extracted or escape at a pressure above atmospheric pressure; b) indirectly contact the discharge steam with clean water, to condense the discharge vapor at a pressure above atmospheric pressure, to produce condensate from the geothermal steam, and to vaporize the clean water and produce clean steam; c) extract from the heat exchanger, non-condensable gases contained in the geothermal steam; d) perform the expansion of clean steam to produce electric power and clean discharge steam; e) condensate the clean discharge steam at a pressure below atmospheric and produce clean condensate; and f) return the clean condensate to the heat exchanger.

10. A method according to claim 9, characterized in that the ratio of electrical energy produced by the expansion of geothermal steam to produce electrical energy and discharge vapor at a pressure above atmospheric pressure, to the energy produced by the expansion of clean steam to produce electric power and clean discharge steam at a pressure below atmospheric is approximately 1: 3.

11. A method according to claim 10, characterized in that the amount of electrical energy produced by the expansion of geothermal steam is changed according to changes in the thermodynamic quality of the geothermal steam.

12. A method for producing electrical energy from geothermal steam having a vapor component and a large quantity of non-condensable gases, characterized in that it comprises: a) carrying out the expansion of geothermal steam in a primary steam turbine, to produce electric energy; geothermal and steam that has undergone an expansion, at a pressure above atmospheric pressure; b) condensing the geothermal steam that has undergone the expansion, in an indirect contact exchanger, to produce geothermal condensate and clean steam; c) extract non-condensable gases from the indirect contact heat exchanger; d) perform the expansion of clean steam in a secondary steam turbine, to produce electric power and clean steam that has undergone expansion, at a pressure below atmospheric pressure; e) condense the clean steam that has undergone the expansion, to produce clean steam condensate; and f) return the clean steam condensate to the indirect contact heat exchanger.

13. An electric power plant according to claim 1, characterized in that the primary steam turbine is a multi-stage turbine having at least one high pressure stage and at least one low pressure stage, mounted on a shaft or shaft , and an electric generator mounted on the shaft or shaft, between the at least one high pressure stage and the at least one low pressure stage, for rotation or rotation at the same speed as the turbine stages.

14. An electric power plant according to claim 13, characterized in that the number of high pressure stages is not greater than three, and the number of low pressure stages is not greater than three.

15. An electrical power plant according to claim 13, characterized in that the rotational speed or rotation of the shaft or shaft is low.

16. An electrical power plant according to claim 15, characterized in that the rotational speed of the shaft or shaft is about 1500 revolutions per minute (RPM).

17. An electric power plant according to claim 15, characterized in that the rotational speed, of the shaft or shaft, is approximately 1800 RPM.

18. An electric power plant according to claim 8, characterized in that the pressure of the geothermal steam, supplied to the primary steam turbine, is approximately 10.5 barA.