Developments in geothermal energy in Mexico—part forty. The future for geothermal energy in Mexico

In Mexico there are many potential geothermal energy sources with a wide range of temperatures. At present high temperature geothermal energy is used to generate electricity. Considerable experience has been accumulated in the exploitation of geothermal energy. Lower grade geothermal heat could be used to generate electricity with organic Rankine cycle plants. There is little industrial exploitation of lower temperature geothermal resources at present even though in the centre of Mexico areas of geothermal activity coincide with industrial zones. However, this situation could change with the use of suitable heat exchangers and heat pumps, particularly absorption systems to supply process heat with very little pollution.     

Developments in geothermal energy in Mexico—part twenty-three. Operation of Cerro Prieto II and III power generation plants

Geothermal plants Cerro Prieto II and III of 220 MW_e each achieved excellent operating conditions during 1987 with plant factors of 0.74 and 0.85, respectively. This demonstrates the operation of large geothermal plants with plant factors higher than have been achieved in Mexican thermoelectric plants.With the total installed capacity in the Cerro Prieto field of 620 MW_e, 14.4 PJ_e (4 TW h) of electrical power have been generated, which represents a saving of 7.55 million barrels of oil.     

Developments in geothermal energy in Mexico—part nineteen. Corrosion in Mexican geothermal wells

The Instituto de Investigaciones Eléctricas and the Comisión Federal de Electricidad have initiated a collaborative study to define the specifications of steels for use in geothermal well construction in Mexico. Tests have been designed to characterize and control identifiable factors affecting corrosion. The study includes three main areas of activity: (a) studies of cases of material failure from several Mexican fields were made; (b) studies of general, localized and stress corrosion of sample coupons exposed to geothermal fluid were made in wellhead pressure chambers; (c) laboratory tests are being carried out under controlled hydrodynamic conditions.     

Developments in geothermal energy in Mexico—part thirty-one. Prediction of geothermal cement durability from field tests

Cement data reported in 1985 by the Geothermal Cements Task Group of The American Petroleum Institute (API) Committee 10 on cements standardization are presented. In order to obtain adequate cement compositions for geothermal environments, the API and National Bureau of Standards (NBS), U.S.A. and the Comisión Federal de Electricidad (CFE), together with the Instituto de Investigaciones Eléctricas (IIE), Mexico, have completed a programme to evaluate 16 cement compositions in the Cerro Prieto geothermal field in both down-hole baskets and in surface chambers.     

Developments in geothermal energy in Mexico—part thirty. Conclusion of the corrosion in mexican geothermal wells project

This paper is complementary to part 19 of this series, in which partial results from the joint IIE/CFE studies were presented. The objective was to define the specifications for steel used in geothermal well construction in Mexico and to characterize and control identifiable corrosion inducing factors. The complete results of corrosion testing in wellhead pressure chambers, down hole chambers and in an autoclave simulation system are included. Also shown are chemical, mechanical and metallographic studies on steels commonly used in Mexican geothermal wells, as well as the main conclusions.     

Developments in geothermal energy in Mexico—part sixteen. The potential for heat pump technology

Mexico possesses large amounts of geothermal brine at temperature which are too low to enable electricity to be generated efficiently and economically. Any system which extracts useful energy from a geothermal source is limited by the effectiveness of the heat transfer between the geothermal fluid, which has a tendency to scale, and the relevant components of the system. A heat pump can be used to maintain a temperature difference between two vessels containing pure water and geothermal brine, which is sufficient to enable pure water vapour to flow continuously from the geothermal brine vessel to the pure water vessel. The hot water produced can then be used to operate an absorption cooling system which can be used to store food. Alternatively a heat pump can be employed to increase the temperature of the hot water to produce low pressure stream.     

Developments in geothermal energy in Mexico—part twenty-five: Operating experience with a geothermal wellhead turbine

After several months of operation of a wellhead 5 MW geothermal turbine, an incident occurred due to the failure of the governor oil pipe joint. The oil tank drained out causing damage to the turbine bearings. Heavy scaling of the first blading stage of the turbine was observed, particularly in the nozzles. Recommendations for the design and remote control operation of the wellhead unit are discussed with reference to the faults found in this case.     

Developments in geothermal energy in Mexico—part eighteen. History of the exploration of the cerro prieto geothermal field

Exploration of the geothermal field of Cerro Prieto started in the 1960's, including the drilling of wells at depths from 1000 m down to 1300 m, which discharged a large amount of geothermal fluid at high pressure. A simple model of the field indicated a suitable productive area of less than 1 km². More wells were drilled in the 1970's, resulting in an expected suitable productive area of 4 km². In 1986, the known suitable productive area was 25 km². The potential of the field was 1000 MW of power, which ensured the continuous production of the 620 MW already installed [1]. Currently, deep drilling is progressing on the eastern parts of the field, including wells 450 m deep which will eventually lead to a better knowledge of the extent and potential of the field through pressure, temperature and production measurements obtained from exploration wells.     

Development in geothermal energy in mexico—part twenty seven: The potential for geothermal organic rankine cycle power plants in Mexico

Mexico possesses large amounts of geothermal energy. Samples from over 800 geothermal surface phenomena indicate that only 1.1% have an estimated reservoir temperature greater than 200°C. Current practice in Mexico is to produce power from such reservoirs using an open flash steam cycle. It is estimated that 4.8% of geothermal resources are in the temperature rangefrom 140 to 200°C which is a suitable range in which to operate Organic Rankine cycle power plants. Organic Rankine cycle power plants have been built in a range of sizes from 10kW_e to 45 MW_e. They have considerable potential for increasing the production of electricity from Mexico's geothermal resources. Organic Rankine cycle plants are discussed together with the conditions for their economic operation.     

Developments in geothermal energy in Mexico—part twenty-nine: Scaling studies at the Cerro Prieto geothermal field

The high silica content (over 900 p.p.m.) of Cerro Prieto geothermal brine causes problems of scaling at the electric power facility. The scaling tendency is a direct function of the silica saturation ratio. Scaling rates of 1–10 mm per year were experienced at low saturation ratios (SR) < 2 and scaling rates of 100–400 mm per year at (SR) > 3. Pilor plant tests satisfactorily predict scaling rates in commercial equipment. Amorphous silica deposited in process equipment can be dissolved by NaOH, KOH and NH₄HF₂. The use of chemical products to remove scale from well liners is a good method of control. The removal of colloidal silica by using 20–30 p.p.m. of lime has been developed.     

Developments in geothermal energy in Mexico—Part twenty. Technical advantages and disadvantages of geothermal well-head units

The technical advantages and disadvantages resulting from locating a steam turbine unit close to a geothermal well-head are presented. The short steam piping system has implications in the design of a well-head turbine. It is concluded that there are some technical differences between large geothermal turbines and well-head units, which may be decisive in the selection of geothermal plant.     

Developments in geothermal energy in Mexico—part thirteen: the operation of surface equipment for geothermal fluid conduction at Cerro Prieto I

At Cerro Prieto I 34.5 PJ_e have been generated and 334 million tonnes of geothermal fluid have been produced. The length of the present system of 300 mm (12 in) to 350 mm (14 in) dia. steam pipelines is 24 km. That of the water pipeline system of 200 mm (8 in) to 400 mm (16 in) dia. pipe is 46.5 km. A total of 32 wells, 41 separators, 51 silencers, 7 steam driers, and 290 200 mm (8 in) to 400 mm (16 in) dia. valves are in operation. Corrosion in the pipelines and other surface equipment has not been a serious problem. The principle maintenance problem has been the cleaning of silica scaling and sediments in pipelines, equipment and channels. Frequent maintenance is necessary in order to maintain the capacity of water pipelines, separators and channels. The well liners and in some cases the deposits themselves have been affected by scaling. Even the small amounts of silica that are carried by the separated steam cause scaling of turbine blades, reducing their capacity.     

Developments in geothermal energy in Mexico—Part thirty-seven. Procedure to diagnose production abatement problems in geothermal wells

A procedure to diagnose cases of production decrease in geothermal wells is presented. Most commonly, a production decrease in geothermal wells is due to: surface pipeline scaling, mechanical damage in the wellbore, entrance of cooler fluids to the producing reservoir layer and reservoir and well pipeline scaling. The procedure, which is presented as a decision diagram, is based in chemical and well production data. It is able to identify the above mentioned causes for a given well. This procedure was successfully applied to 17 wells from the Cerro Prieto geothermal field. In addition, a silica deposition rate parameter, Rd, was designed. It can be used as a forecasting tool for well scaling. It is proposed that this parameter is important in deriving suitable production strategies to minimise the effect of silica scaling processes in the reservoir.     

Developments in geothermal energy in Mexico—part thirty-six. The commissioning of a heat pump assisted brine purification system

Any system which extracts useful energy from a geothermal source is limited by the effectiveness of the heat transfer between the geothermal fluid, which has a tendency to scale, and the relevant components of the system. A heat pump can be used to maintain a temperature difference between two vessels containing pure water and geothermal brine which is sufficient to enable pure water vapour to flow continuously from the geothermal brine vessel to the pure water vessel. A mechanical vapour compression heat pump using R114 as the working fluid and designed to deliver more than 50 kW of heat has been incorporated in a brine purification system at the Los Azufres geothermal field. This system has been successfully commissioned and is operating as designed and theoretically predicted.     

Developments in geothermal energy in Mexico—part thirty-nine. Extraction of useful heat and silica removal from geothermal brine utilizing liquid fluidized bed heat exchangers

Liquid fluidized bed heat exchangers can be utilized for the recovery of heat from geothermal brine in order to avoid scaling. At the same time, these heat exchangers remove silica from the geothermal brine. A new parameter, obtained from the bed expansion and referred to as the porosity of transition, is defined. This parameter contributes to a better understanding of systems utilizing liquid fluidized bed heat exchangers. From the model proposed by Goto [J. Phys. Chem.60, 1007–1008 (1956)] for silica polymerization and modified by Axtmann [Geothermics15, 185–191 (1986)] for silica removal, the rate of reaction constant is expressed as a function of silica equilibrium monomer concentration (solubility).     

Developments in geothermal energy in Mexico—part thirty-four. Numerical steady-state simulation of the steam supply system of the cerro prieto geothermal plant

The philosophy used in the mathematical modelling of the steam supply network of Cerro Prieto geothermal power stations is described. In order to form the simulation model of this system, mathematical models were developed for: the surface equipment such as separators, pressure control stations, steam turbines, low and high pressure interconnections, purges and wells. With the above mentioned models a computer programme was produced which operating conditions in the steam supply system.     

Developments in geothermal energy in Mexico—Part thirty-two. Supply and demand perspectives for the year 2000

The participation of geothermal energy in the national electric power supply has steadily increased since its beginning in 1973 to a value of 50.4 PJ yr⁻¹, 5.4% of the total electric demand. The activities programmed by the Mexican government indicate that for the year 2000, an estimated 4.0% of the electricity demand could be satisfied by geothermal energy. A larger participation of geothermal and other alternative energy sources is needed in order to have a smooth energy transition and to continue exporting hydrocarbons beyond the year 2000. It is concluded that it is possible to achieve a geothermal energy participation in that year of around 5% of the net internal supply, as 13% of the electric power demand and 3% of the thermal demand.