WO2007112526A1

WO2007112526A1 - System and method for biogas utilization

Info

Publication number: WO2007112526A1
Application number: PCT/BR2007/000077
Authority: WO
Inventors: Alexandre Kemenes; Luzia Gomes Ferreira Pavani; Sylvia Souza Forsberg; Maria da Consolação Gomes Cunha Fernandes TAVARES
Original assignee: Alexandre Kemenes; Luzia Gomes Ferreira Pavani; Sylvia Souza Forsberg; Tavares Maria Da Consolacao Go
Priority date: 2006-03-31
Filing date: 2007-03-29
Publication date: 2007-10-11
Also published as: BRPI0605397B1; BRPI0605397A

Abstract

System and method for biogas utilization, being such biogas derived from deep waters of the lakes formed by the flooding of the land occurring from the construction of dams to produce hydroelectric energy. The invention has the objective of reducing the emissions of methane to the atmosphere, therefore substantially decreasing global warming by the greenhouse effect, as well as the objective of utilizing such biogas to generate energy. The biogas, released in the hydroelectric power plants during the sudden decompression of the waters that flow through the turbines, is collected during and after its flow through the turbines and it could be stored for later use or burned at site in thermoelectric energy generating facilities or even in other locations, should it be transported by pipelines.

Description

SYSTEM AND METHOD FOR BIOGAS UTILIZATION

Field of the Invention

The present invention refers to the utilization of biogas from the bottom waters of hydroelectric reservoirs, during and after such water flows through the turbines of hydroelectric power plants, to generate energy and reduce the emission of methane to the atmosphere, thereby diminishing the contribution of these systems to global warming. Background of the Invention

Biogas is a variable mixture of biogenic gases, mainly comprised by methane and carbon dioxide, which is produced from the anaerobic decomposition of organic material. In the specific case of lakes formed by the flooding of land in order to build dams for the generation of hydroelectric energy, such reactions occur when anoxic conditions are present, regardless of depth. Generally, stagnant waters, near the bottom and isolated from the atmosphere, present favorable conditions for the genesis of the methane gas. While methane is relatively insoluble in water at atmospheric pressure, it dissolves very well in deep pressurized waters.

This tendency is indicated in Fig. 1, which shows the relation between methane concentration and hydrostatic pressure at different water depths. This graph describes the average relationship encountered above Balbina dam, based on regular measurements made during a full year. As can be seen, starting at a depth of about 20 meters, which is equivalent to 3 atmospheres of pressure, methane becomes very soluble in water. Thus, biogas is naturally generated and pressurized in the bottom waters of a hydroelectric reservoir.

As this water flows through the dam's hydroelectric turbines (through flow) and is discharged downstream (discharge), there is a rapid drop in hydrostatic pressure and a large part of the biogas is released to the atmosphere. Since it is released in a limited area, this gas can be easily collected, stored and burned for the generation of energy on site or transported to be used on other sites.

Taking the Balbina Hydroelectric Dam (Brazil) as a first example, an estimated 297,926,000 cubic meters of biogas was released through the turbines during the year of 2004. As the characteristics of dams differ, the concentration of methane in the biogas also varies from dam to dam and also according to the year. In the specific case of the biogas released by the Balbina Hydroelectric Dam, the percentage of methane in the gaseous mixture, in 2004, was estimated in 43%. This value is inferior to the minimum concentration required for a direct burn (45%), so the methane has to be purified or enriched in the mixture before burning it, should the objective be the generation of energy. However, in other dams, such as the Petit Sault in the French Guiana, greater concentrations of methane were found in biogas released downstream from the turbines, allowing a direct burn. Evidently, whichever the initial concentration of methane in the biogas may be, the increase of its concentration in the mixture will result in greater heat power of the gas, increasing the global efficiency of the process, be it during the burn, the storage or the pumping of the gas through pipelines to other sites. As previously stated, the components of biogas contribute to global warming through the greenhouse effect. While the carbon dioxide concentration in biogas is often greater than the methane concentration, the contribution of the latter to the greenhouse effect is much greater, since the atmospheric heating potential of methane is about twenty one times greater than that of carbon dioxide. In order to calculate the potential contribution of any gas to the global warming, the flux is generally converted to an equivalent of carbon dioxide, using conversion factors that consider the molecular weight and the thermal potential of each gas. In the particular case of the methane, this factor is twenty one. Applying this factor, the annual contribution of the emissions downstream from Balbina Dam to the global warming, including the CO2 and the CH4 fluxes, was estimated to be 2,135,000,007 kilograms of CO2 equivalent carbon. Objectives of the Invention According to the aforementioned facts, one of the objectives of the present invention is the utilization of methane or of biogas derived from hydroelectric systems to generate thermal energy with other industrial applications.

A second objective is to provide a system that reduces the emissions of methane into the atmosphere in order to substantially reduce global warming by the greenhouse effect. This reduction could be converted into carbon credits for the country involved. Brief Description of the Invention

The aforementioned objectives, as well as other objectives, are attained by this invention based on the fact that the biogenic gaseous mixture (biogas), composed mainly of methane and carbon dioxide, present in the deep waters of dam reservoirs, could be efficiently collected during and after the flow of these waters through the turbines of a hydroelectric power plant and used to generate energy. This operation would reduce the atmospheric emissions of methane and thus reduce the contribution of the hydroelectric power plants to global warming.

According to one characteristic of the invention, means of collecting the gases generated by the sudden decompression of the water used in the generation of hydroelectric energy are provided. According to another characteristic of the invention, such means are located downstream of the water discharge nozzles, after the flow of the water through the turbines or in pipelines for the elimination of the biogas during its flow through the turbines. According to yet another characteristic of the invention, said means would comprise collection chambers that would avoid the direct release of the biogas to the atmosphere.

According to another characteristic of the invention, said collection chambers would be followed by means of treating the biogas in order to increase the methane concentration. In the specific case of biogas with a methane concentration of over 45%, this treatment would be optional.

According to yet another characteristic of the invention, the methane is stored and could be transported to remote locations through pipelines. According to another characteristic of the invention, the methane could be burned at site in facilities that generate thermoelectric energy or in other locations should it be transported.

According to yet another characteristic of the invention, the carbon dioxide could be used in the manufacturing of a series of manufactured goods.

Brief Description of the Drawings

The advantages and further characteristics of the invention will become more evident on its detailed description of its preferred embodiment and drawings, which are made as a non-limiting example. Figure 1 shows the variation of the average concentration of methane in relation to hydrostatic pressure and depth at the Balbina hydroelectric dam in 2004.

Figure 2 illustrates, in a simplified manner, a cross-section view of a dam and its corresponding hydroelectric power plant, as well as the biogas collection, treatment, storage and utilization system, according to the principles of the present invention. Detailed Description of a Preferred Embodiment

According to the aforementioned, the present invention is related to the utilization of biogas, derived from the waters of hydroelectric dams during the turbine through-flow and discharge, to generate energy and reduce the emissions of the gases that cause the atmospheric greenhouse effect. The concept includes the following elements:

- A hydroelectric power plant, either planned or pre-existing; - A means of collecting biogas;

- A means of purifying/enriching methane, which could be mandatory or optional depending on the concentration of methane in the biogas;

- A means of storage and/or transporting the gas, enriched or not;

- A means of generating electrical energy from the biogas or from the purified methane.

According to Fig. 2, a hydroelectric power plant is constituted by a dam (11) for restraining the water (12) upstream, comprising at least one hydraulic turbine (13) that is coupled to a generator (14) by means of an axle (15). The upstream water, under pressure, penetrates the pipes (16) that feed the turbine and, after through-flow, exits the turbine through a discharge nozzle (17) at a significantly reduced pressure, which is equal to the atmospheric pressure. The reduction of the pressure that occurs during the through-flow of the water in the turbines results in the release of the biogas which, according to what is shown on the graph fo Fig. 1 , is relatively insoluble in water at atmospheric pressure.

Different methods can be used to separate, collect, store, purify and burn the biogas, in order to generate energy with more or less efficiency.

Should the percentage (per volume) of methane in the biogas be greater than 45%, it could be burned directly or processed to concentrate or purify the methane in the mixture which will increase the heat energy potential of the gas. Should the percentage of methane be less than 45%, it will be necessary to purify or concentrate the methane in the biogas before burning it. The collected biogas or the methane derived from the biogas could be burned to generate energy near the source hydroelectric power plant or it could be transported to be used in other regions. The electrical power generated near the collection site could be transmitted using the pre- existing power lines.

Old and new hydroelectric power plants could be planned or retrofitted for the collection and utilization of biogas.

According to the principles of the invention and according to what is shown on Fig. 2, means of collecting (28) the gas released from the turbines are provided. Such gas is sent to a collection chamber (18) that also collects the biogas immediately downstream from the turbines, which is released from the surface of the water. The collected biogas is then pumped, through the pipeline (19), to an optional purifying and concentrating device (21), which increases the concentration of the methane in the biogas. In the illustrated embodiment, the enriched gas, which has a high methane concentration, is sent to a reservoir (22) for its later utilization as fuel in a thermoelectric generation device (23), with the produced electrical power being distributed through the existing distribution network (24). Another utilization option comprises the transport of the methane or the biogas to other locations, by means of its pumping through a pipeline (not shown).

The supply of a gas reservoir (22) allows that the methane or biogas be used as an auxiliary source of electrical power at times of peak power demand, enabling greater efficiency in the management of the water resources, as well as a lower cost of the generation equipment, since it does not have to be sized to supply the demand peaks.

The burning of the gaseous mixture and of the purified methane by the aforementioned process will release mainly carbon dioxide and water to the Earth's atmosphere through the exhausts (29 and 30). As the potential atmospheric warming of carbon dioxide is about twenty one times less than that of methane, this will significantly reduce the contribution of the power plant to global warming and such reduction can be up to 75%. The carbon dioxide released by the burning of biogas or methane

(29), and that isolated during the optional purification of the biogas (30) could be stored and/or transported and used in the manufacture of a series of products, such as carbonated soft drinks, among others, without the consumption of fossil fuels, which are normally used in the production of carbon dioxide.

Even though the present invention was described based on a specific embodiment, it is understood that modifications can be introduced to the proposed system without departing from the scope of the invention, which is defined and limited by the following set of claims.

Claims

1- SYSTEM FOR BIOGAS UTILIZATION, said gas being released in a hydroelectric power plant, during the sudden decompression of the water that flows through the turbines, characterized in that it comprises means of collecting such gases during and after its flow through the turbines, being such gases used by thermoelectric energy generating devices.

2- SYSTEM, according to claim 1 , characterized in that it comprises means of purifying and enriching the methane in the collected gas, should the concentration of methane therein be less than 45%.

3 - SYSTEM, according to claim 1 , characterized in that it comprises gas storage means.

4- SYSTEM, according to claims 1 , 2 or 3, characterized in that it comprises optional means of pumping the biogas as well as a pipeline to transport such gas to remote locations.

5- METHOD FOR BIOGAS UTILIZATION, being such gas released during and after the passage of reservoir bottom waters through the turbines of hydroelectric power plants, using the system of the previous claims 1 to 4, characterized in that it comprises the collection of the biogas released by the waters used by the turbine followed by the treatment of said biogas.

6- METHOD, according to claim 5, characterized by the fact that such treatment comprises the increase of the methane concentration contained in the referred biogas, should it be less than 45%. 7- METHOD, according to claims 5 or 6, characterized by the fact that such treatment comprises the storage of the biogas in a reservoir.

8- METHOD, according to claims 5 or 6, characterized by the fact that such treatment comprises the optional pumping and transportation of the biogas to a remote location through a pipeline. 9- METHOD, according to claim 5, characterized by the fact that such treatment comprises the combustion of such biogas in a thermoelectric energy generating device.

10- METHOD, according to claim 9, characterized by the possibility of said combustion be carried out in times of peak electric energy demand.