Method and apparatus for producing a gas containing CO2, in particular for CO2-fertilization in the greenhouse horticulture.

Abstract: The invention relates to a method for producing a gas containing CO₂, in particular for CO₂-fertilization in the horticulture. According to the invention at least a part of the exhaust gasses produced by an installation for central electricity supply is seperated and entered into a distribution system in compressed and cooled state.

Description: The invention relates to a method as defined in the first part of claim 1. In modern greenhouse horticulture it is common practise to improve plant growth by applying CO 2 -fertilization, involving passing a gas containing CO 2 through the greenhouses. Individual market gardens are usually equipped with a gas-fired combustion device for the production of heat within the greenhouse and it has become common practise to pass the exhaust gases of the combustion device into and through the greenhouse to increase the CO 2 content therein. The demand for heat, however, does not always correspond with the demand for CO 2 . A method for the type above referred to is disclosed in DE-A-39 37 012, describing the principle of isolating a part of the exhaust gas flow of a gas-fired combustion device and passing the same after cooling into and through a greenhouse so as to cover the CO 2 demand. The type of combustion device has not been mentioned. Document US-4-434 613 discloses a gasturbine/steam turbine plant for producing electricity and CO 2 and N 2 in liquid state. Document US-4-899 544 discloses the placing of an electricity producing plant at a CO 2 -consumption site, with the main purpose to satisfy the demand for CO 2 at such site, which may be an oil recovery site, a site where foods are to be refrigerated or a site for beverage carbonisation. It is an object of the invention to provide for an economic way to cover the CO 2 demand for CO 2 -fertilization in the greenhouse horticulture. In accordance with the invention this aim is achieved by the measures defined in the second part of claim 1. Extensive research and calculations have shown that due to 1. the increase of the CO 2 -content of the isolated exhaust gases by treatment of the latter as combustion air in the auxiliary combustion device and 2. the compression of the enriched exhaust gases up to e.g. 10 bar enable CO 2 -delivery from a central electricity plant to greenhouses through a distribution network of pipes of relative reduced diameter and consequently at a relatively low price. Furthermore processes of cleaning the exhaust gases for environmental purposes can be carried out easier and more economical at a central production site than at the sites of the market gardens individually. The invention also relates to an electricity production plant as defined in the first part of claim 4. Such a plant, having as its main purpose the production of electricity is commonly known and may be considered as disclosed in document US-A-4.434.613. It is a further object of the invention to provide an improved electricity production plant, which can also cover the CO 2 demand for CO 2 -fertilization in the greenhouse horticulture at an economically acceptable cost price. This aim is achieved by the measure as defined in the second part of claim 4. Further features of the invention will be explained below by way of example with reference to the accompanying drawing. The drawing shows a diagram of a modern electricity production plant, which is primarily adapted for the production of electric energy (by a generator) and heat (by means of a condenser) and which is, according to the invention, further designed for delivering a gas containing CO 2 . The illustrated plant comprises an usual combination of a gas turbine unit A, a steam turbine B and an electrical generator C. The gas turbine unit A comprises the gas turbine 1, the air compressor 2, having an air inlet 3, the combustion chamber 4, which is fired e.g. with natural gas, and the steam generating device 5, having heat exchanger bundles 6 and an exhaust pipe 7 for exhaust gasses. The steam turbine B comprises a high pressure section 8 and a low pressure section 9, the output of which is connected to a condenser 10 by means of a pipe 11. The steam turbine B is supplied with steam, that is generated by passing the condensation water leaving the condenser 10 through pipe 12, through the heat exchanger bundle 6 in the steam generating device 5. Sofar the plant is of a well-known concept. According to the invention, a "branch-off pipe" 13 with a ventilator 14 is connected to the exhaust pipe 7, by which at least a part of the exhaust gasses, which otherwise would be emitted to the environment through pipe 7, can be isolated and brought into a compressed state by means of the exhaust gas compressor D for delivery into a distribution network (not shown) through a pipe line 15. The compressor D includes a low pressure stage 16 and a high pressure stage 17. Between the stages 16 and 17 and after the stage 17 the exhaust gases are passed through cooling heat exchanger bundles 18 and 19, having water separators, repectively. Within the coolers 18 and 19, the temperature of the compressed exhaust gasses can be lowered to 70° C or less, when for example water for central heating is used as a cooling medium. In this way, a part of the energy used for compressing the exhaust gasses, can be recovered. Before the isolated exhaust gasses are supplied to the compressor D, the seperated exhaust gasses are first pretreated in an auxiliary combustion device E to increase the CO 2 -content. To that end the exhaust gasses are used as combustion air in a combustion device E, adapted for firing e.g. natural gas. The combustion device E is provided with heat exchanger bundles 20 and 21. The amount of natural gas to be fired in the auxiliary combustion device E can be regulated in such a way, that the remaining amount of O 2 in the exhaust gasses will be consumed almost totally. In this way, the CO 2 -content, which is normally about 3,2 vol.%, can be almost tripled. Due to the increased CO 2 -content the required amount of compression energy will be substantially reduced and accordingly the costs for distribution will be correspondingly reduced. The use of the relatively low-oxygen exhaust gasses from the steam generating device 5 as combustion air in the auxiliary combustion device E results in a lowering effect on the NO x -production, which is not only advantageous from an environmental-technical point of view, but also has an advantageous effect on the use as fertilization gas. The heat produced in the auxiliary combustion device E is used for the intermediate heating of the steam in the main steam turbine B by passing the steam from the high pressure section 8 through the heat exchanger bundle 21 in the auxiliary combustion device E before supplying it to the low pressure section 9. This will increase a power of the steam turbine B accordingly. An other portion of the heat produced in the auxiliary combustion device E is used to produce additional steam, which is supplied to an auxiliary turbine 22 which drives the compressor D. The condensation water of the condenser 10, to which the output of the auxiliary steam turbine 22 is connected, is therefore passed through the heat exchanger bundles 20, which bundles are connected to the steam inlet pipe 23 and 24, to the high pressure section 8 of the main steam turbine and the auxiliary turbine 22 respectively.

Claims: A method for producing a gas containing CO 2 for CO 2 -fertilization in the greenhouse horticulture by making use of at least a part of the exhaust gases of a combustion device (4), characterized in that the exhaust gases are taken from an electricity production plant (A-C), in that said part of the exhaust gases is supplied to an auxiliary combustion device (E) in which the air contained in said part of the exhaust gases is consumed as combustion air and in that the exhaust gases of said auxiliary combustion device (E) are brought in a compressed and cooled state suitable for direct supply into a distribution network for CO 2 -fertilization. A method according to claim 1, characterized in that the exhaust gases of said auxiliary combustion device (E) are compressed to a pressure of approximately 12 bar. A method according to claims 1-2, characterized in that at least a portion of the heat produced by the auxiliary combustion device (E) is used for producing steam that is used as a power source to compress said exhaust gases. An electricity production plant, comprising in combination a gasturbine (A), a steam generator (5) in which the heat contained in the exhaust gases from the gasturbine (A) is used to produce steam, a steam turbine (B) with a condenser (10) supplied with steam from said steam generator (5), an electric generator (C) connected with said gas and steam turbines (A and B), wherein said steam generator (5) comprises an outlet (7) for cooled exhaust gases, a branch pipe (13) in said outlet (7) and a compressor (D) connected to said branch pipe for subsequent distribution of the respective exhaust gases in a compressed state, characterized in that an auxiliary combustion device (E) is provided in said branch pipe (13), the outlet of said auxiliary combustion device being connected to said compressor (D). An electricity production plant according to claim 4, characterized in that the auxiliary combustion device (E) comprises one or more heat exchanging pipe bundles (21), which are taken up as an intermediate heating stage in the steam circuit between stages (8 and 9) of said steam turbine (B). An electricity production plant according to claims 4-5, characterized in that the auxiliary combustion device (E) comprises one or more heat exchanging pipe bundles (20), which form part of the steam/condensation circuit of an auxiliary steam turbine (22) driving said compressor (D). A plant according to claim 6, characterized in that the outlet (11) of the steam turbine (B) and the outlet of the auxiliary steam turbine (22) are connected to a common condensor (10). A plant according to claims 4-7, characterized in that the compressor (D) is a multistage compressor, whereby in the exhaust gas connection between the stages (16, 17) and in the outlet of the last stage a heat exchanger (18; 19) is provided for cooling the exhaust gases.

Inventors: HYLKEMA HETTE KERST, HYLKEMA, HETTE KERST
Applicants: ZUID HOLLAND ELECTRICITEIT, N.V. ELECTRICITEITSBEDRIJF ZUID-HOLLAND
Application year: 1992
Main classification: B01D53
IPC codes: A01G9, B01D53