WO2010074570A1

WO2010074570A1 - Greenhouse using flue gas

Info

Publication number: WO2010074570A1
Application number: PCT/NL2009/050793
Authority: WO
Inventors: Gerrit Vermeer
Original assignee: Newplant B.V.
Priority date: 2008-12-24
Filing date: 2009-12-22
Publication date: 2010-07-01
Also published as: EP2373151A1; NL1036368C2

Abstract

Device for the extraction of CO₂ that is present in flue gas. The aim is to extract the CO₂ present in flue gas in order to utilize it later, for example in a greenhouse. The presence of other gases such as hydrocarbons or nitrogen-oxygen compounds (NO_x), is undesirable in this connection. It is therefore proposed to absorb the CO₂ in a water circulation system and to release it at a later stage. It has been found that a number of the above mentioned harmful gases are less easily absorbed than CO₂. The absorption can be achieved by exposing the flue gas to a water spray. The release can be brought about by introducing the water into a tank. The CO₂ is preferably separated from the water by placing the water under reduced pressure, for example with a Venturi tube.

Description

GREENHOUSE USING FLUE GAS

The present invention relates to a device for the extraction of CO₂ that is present in a flue gas.

In the prior art, for example in horticulture, combined heat and power plants are used in which for example natural gas is used to drive a generator. This generator generates electricity and releases heat and CO₂ as additional products. The heat generated can be used to heat a cultivation area, such as greenhouses, while the CO₂ acts as a growth promoter for certain plants. The electricity can be used for lighting cultivation areas and/or it can be fed back into the national grid.

It is particularly the use of CO₂ for promoting the growth of certain plants that is of interest here. However, it has been found that not only CO₂ is present but also hydrocarbons (such as ethylene) and nitrogen compounds (such as NO_x), which have proved harmful to certain plants.

To solve this problem, filtering devices are used, wherein the gas is passed through channels where harmful substances are bound with the aid of chemical reactions. However, both the mounting and the maintenance of the filters are expensive, and these installations only remove some of the harmful substances, so the CO₂ obtained in this way can only be used where less sensitive plants are being grown, and its use in closed greenhouses is less attractive. Improved installations have been proposed as an alternative, but they are much more expensive in use.

GB Patent No. 855,543 discloses a purification installation for flue gases that operates at an elevated pressure. The flue gases are passed through columns at an elevated temperature and pressure and various substances are introduced. Such a device is particularly suitable for use in the chemical industry.

The aim of the present invention is to provide a cultivation assembly consisting of a cultivation area in combination with an electricity generator, where the said generator is operated by burning a fossil fuel, and the flue gases can be used in the cultivation area.

This aim is achieved by means of a cultivation assembly comprising a cultivation area with plants arranged therein, and a heat and electricity generator, with a CO₂ delivery pipe discharging in this cultivation area, wherein the flue-gas outlet of said generator comprises a device for the extraction OfCO₂ present in the flue gas, which device comprises a flue-gas channel that is connected to the inlet of the flue gas to be purified, which flue-gas channel accommodates a water spraying system, where said flue-gas channel comprises a water outlet and a gas outlet, said water outlet is connected to a closed separating tank, and means of water circulation are connected to said separating tankjSaid means of water circulation ensuring the reduction of the pressure on the water circulating therethrough, wherein said separating tank is connected to said water spraying system by a return pipe and the top of said separating tank has a gas outlet for the CO₂ emerging from the said separating tank, and the gas outlet of the separating tank is connected to said CO₂ delivery pipe.

According to the present invention, the gas coming from a combined heat and power plant is exposed to a water spray. It has now been found surprisingly that, when a sufficient amount of water spray is introduced, the CO₂ is absorbed in the water, while vapours containing NO_x and hydrocarbons, such as ethylene, are taken up to a much smaller extent. The water stream coming from the water spraying system therefore essentially comprises pure CO₂. This Cθ2-containing water is then passed into a separating tank, and the pressure of the water is reduced in or near this separating tank. Owing to this pressure reduction, the CO₂ is liberated and rises to the top of the separating tank, so it can then be passed into the cultivation area. It is also possible to use a number of separating tanks, which can be connected in series.

This system operates at a low pressure, such as 1 atm, and at a low temperature, such as 40-50⁰C, which makes it possible to combine it with a flue-gas condenser. This represents an enormous saving of cost. The flue-gas condenser can also be of a two- stage construction, where condensation in the second stage is optimized by the lower temperature, and the efficiency is increased further. It is also possible to extract the heat directly in the second stage with gas-liquid exchange, so that the temperature of the water drops even further, and therefore the amount of heat recovered by condensation increases.

A second advantage of this is that the second stage can use a process for binding the excess CO₂ in the flue gases, for example by forming CaCOs.

Another advantage of this installation is that the heat and the CO₂ can be used at different points in time in the greenhouses. The heat can be utilized at night, when it is colder, and the CO₂ can be utilized for promoting plant growth during the day, when heat is less desirable, owing to the presence of insolation. In addition, the temperature will also be relatively low.

The present invention makes it possible to construct a combined heat and power plant more simply. The fact is that, in the prior art, the efficiency of such generators, which burn mainly natural gas, is raised by cooling the emerging flue gas in a first stage and then condensing it.

Such a condenser is not needed according to the present invention, since the water spraying system described above ensures such a reduction in the temperature of the flue gas that a separate condensation stage can be dispensed with. The generator will produce not only CO₂, but also electricity and heat (or cooling) energy. These can be utilized in the cultivation area or used for domestic purposes, or else they can be put to some other use.

According to another advantageous embodiment of the invention, an inductively operating device can be arranged in the return pipe between the separation tank and the water spraying system. An example of this is the use of a coil, the idea being to subject the water to an electromagnetic field and electrolysis under the influence of a variable frequency. It has been found that as a result the CO₂ present in the flue gas can be taken up in large amounts, due to the changing physical characteristics of the water, after which it can be released into a separating tank. The contact between the water and the flue gases can in principle be ensured by any method. For example, the water can be sprayed inside a space.

According to a particular embodiment of the invention, the flue-gas channel where the water vapour is atomized can be constructed of a number of tubes or pipes arranged side by side. Each tube or pipe accommodates a number of water sprinklers. Water and gas can be discharged together from each of these tubes or pipes. It is also possible to place a number of spray pipes in a larger channel. The system described above can be operated by one or more pumps. These consume relatively little energy, so that large amounts of water can be circulated at a low cost. A considerable amount OfCO₂ can therefore be taken up and then given off.

The spraying of the gas flowing through the tubes or pipes also has the advantage that the residual heat present in the flue gas is absorbed by the water. This heat can then be put to further good use with heat exchangers. This method further increases the energy efficiency of the device. In addition, more water vapour condenses out of the flue gas, so the efficiency is increased further still.

The water circulation means ensure both the spraying of the water and the reduction of the water pressure. It should in principle be possible to use a simple pump, in which case the water releases its CO₂ content at the suction end, due to the reduced pressure prevailing there. According to a particular embodiment of the invention, this effect can be further improved by arranging a Venfuri tube in the water circulation means. As a result of this, the water is compressed and expanded, with CO₂ being released during expansion. This^* system can be further improved by connecting a gas pipe to the constricted part of the Venturi tube. More especially, this gas pipe is either open to the surroundings (with supply of air from the inside or the outside), or it is connected to the top of the separating tank, so that air is supplied to the latter. This promotes the release OfCO₂. According to a particular embodiment, means for generating turbulence in the water can be provided. More especially, these means can be in the form of blades or the like and fitted either inside or upstream of the Venturi tube. This increases the efficiency of the CO₂ release. According to a particular embodiment of the invention, a substance is added to the water to separate the undesirable substances that have been taken up in it. An example is titanium dioxide, which renders NO and NO₂ harmless when exposed to UV light.

It is of course possible to filter the released CO₂ during its transit from the separating tank to the site of use with any filter known from the art.

In addition, excess CO₂ can be bound by adding for example Ca, so that the compound CaCθ3 is formed. Other substances that are known to lower the reduction of harmful substances in the flue gases can also be added. This can be achieved by using a second, parallel storage tank whenever sufficient CO₂ is present. The means of heat discharge are then also connected to the second tank.

The invention is explained in more detail below with an embodiment illustrated in the drawings, where

Fig. 1 is a schematic representation of a cultivation assembly according to the present invention; Fig. 2 is a more detailed drawing of the separating tank according to the present invention; Fig. 3 is a detail of the water circulation means; and

Fig. 4 is a variant of the device shown in Fig. 1.

The cultivation assembly as a whole according to the present invention is denoted by 1 in Fig. 1. It consists of a prior-art greenhouse 30 or another type of cultivation area, and a combined heat and power plant denoted by 2. In this example, the combined heat and power plant is powered by gas, which is fed into it through pipe 3, but other kinds of fuel can of course also be used. The combined heat and powerplant generates heat and electricity and flue gases. The electricity is removed through pipe 28, heat is educted through pipe 27, and the flue gases are removed through outlet 5.

Since it is desirable to extract the CO₂ present in the flue gases for use in the cultivation area 30, the prior art employs complicated and costly purification installations. The present invention aims at providing a cheap device for the purification of the gases coming from outlet 5. This device as a whole is denoted by 4. Outlet 5 discharges into a number of flue-gas channels 6 arranged side by side. These channels have a length of for example 20 metres and consist of a plastic material. Commercially available pipes with a diameter of for example a few tens of centimetres can be used. Each flue-gas channel 6 contains a number of water sprinklers 7, which are fed from a conduit 9. The flue-gas channels 6 are somewhat inclined, so that the water emerging from the sprinklers 7 flows towards the water outlet 11, which is common to all the flue-gas channels 6. A common flue-gas outlet 8 is also provided (but this can also be arranged individually).

A number of separating tanks 12 with a volume of for example some tens of cubic metres are set up in series. The water outlet 11 discharges into the first of these tanks 12, and is released via the outlet 34 into the inlet 35 of the next tank. In this example, the discharges of the outlet 11 and of the inlet 35 are shown at the top of each tank 12, but it is also possible to couple the water outlet 11 and the inlet 35 with the separating tank 12 at a different point. Each separating tank 12 contains a quantity of water, and the top of the water level is denoted by 13. In addition, each separating tank accommodates a circulating system 14, which will be described hereinbelow in detail. The separating tanks 12 are connected to one another both at the top and at the bottom. CO₂-rich gas is present above the water level 13 and is passed via the tanks connected in the downstream direction into a common conduit 23 and to a fan 24 and finally into a conduit that blows the CO₂-OCh gas into the greenhouse 30.

The tanks 12 are also in communication with conduit 9, which contains a pump 10. A closed system is formed for water circulation by separating tank 12, conduit 9, pump 10, flue-gas channels 6 and water outlet 11.

The water present in the separating tanks 12 can be circulated through pipes 22 connected to them. Each of these conduits is fitted with a heat exchanger 31 , and the heat derived from each of these is conveyed along a conduit 32 for use e.g. for heating a cultivation area or another system in a way not illustrated here in more detail.

The electrical cable leading from the combined heat and power plant is connected to a lighting system 26 situated in the cultivating premises. Excess electricity can be fed into the national grid by cable 33. Heat is conveyed by conduit 27 to a heat exchanger 29, set up in the cultivating premises 30.

Figs. 2 and 3 show details of the separating tank and the circulating system 14, respectively. It can thus be seen that each water circulation system 14 consists of a pump 15 and a Venturi tube that is connected either upstream or downstream thereof. The Venturi tube has an inlet 17, an outlet 18 and a constricted part 19 in between. One or more openings 20 lead into this constricted part, where reduced pressure prevails, and are in communication with a conduit 21 , which is connected in this example to the space above the water level 13.

The above-described device for the purification of gas operates as follows:

The flue gas that contains CO₂, NO_x and hydrocarbons such as ethylene and emerges from the combined heat and power plant 2 is introduced into the flue-gas channels 6 through conduit 5. It is brought into contact there with water that is sprayed by the sprinkler 7. Mainly CO₂, without NO_x and hydrocarbons, is absorbed. These substances are removed through the flue-gas outlet 8. The flue gas is cooled by the spray, that is to say, the water in it condenses. This heats the circulating water that is used for spraying. This dispenses with a downstream condenser in the flue-gas outlet. The water, which contains as large a portion of COa as possible is led into the separating tanks 12 through conduit 11. It is then brought into circulation by the circulation system 14. Water and CO₂ are separated from each other by means of reduced pressure prevailing in the Venturi tube 16. This process is further promoted by the introduction of a gas through conduit 21. The released CO₂ rises through the water to above the water level 13, from where it can be passed into a cultivation area in the way described above. As the flue gas is exposed to a water spray, the water will pick up heat from it, which can be recovered by the heat exchangers 31 for further use.

Fig. 4 shows another variant of the invention, which is largely like the one shown in Fig. 1 , so it is provided with the same reference numbers. However, conduit 9 accommodates here a device which is denoted as a whole by 85, which device consists of a frequency regulator 87 and a coil 86 that generates a magnetic field and is located at or around the conduit 9. The coil 86 is fed with a variable frequency with regulator 87. This has been found to bring the recycled water into a state that ensures not only a better uptake of CO₂ during spraying but also the absorption of other undesirable substances such as NO_x or sulphur compounds. If a relatively clean fuel is used, the increase in the absorption OfCO₂ by the sprayed water is particularly important. This additional amount of absorbed CO₂ is then released in the various separating tanks.

On reading the above description, the person skilled in the art will be able to think of variants which also lie within the scope of the following claims. For example, it is possible to utilize the purification for other installations, that is to say, not or only partly in combination with a cultivation area. Any kind of plant, including algae, can of course be grown in the cultivating premises. Furthermore, additional filters or purification installations can be used. Moreover, the separation of water and CO₂ can be further promoted by means that increase turbulence.

Claims

1. Cultivation system comprising a cultivation area with plants arranged therein, and a heat and electricity generator, with a CO₂ delivery pipe discharging in said cultivation area, wherein the flue-gas outlet of said generator comprises a device for the extraction OfCO₂ present in a flue gas, said device comprises a flue-gas channel that is connected to the inlet of the flue gas to be purified, said flue-gas channel accommodates a water spraying system, wherein said flue-gas channel (6) comprises a water outlet (11) and a gas outlet (8), said water outlet is connected to a closed separating tank (12), and water circulation means (14) are connected to said separating tank, said water circulation means providing the reduction of the pressure on the water circulating therethrough, wherein said separating tank is connected to said water spraying system by a return conduit and the top of said separating tank has a gas outlet for the CO₂ emerging from said separating tank, and the gas outlet of the separating tank is connected to said CO₂ delivery pipe.

2. Cultivation system according to Claim 1 , wherein the said flue-gas channel is constructed for low pressure.

3. Cultivation system according to Claim 1 or 2, wherein said cultivation area is provided with a lighting system operated by electricity obtained from the said generator.

4. Cultivation system according to any one of the preceding claims, wherein said cultivation area is provided with heating produced by heat obtained from said generator.

5. Cultivation system according to any one of the preceding claims, wherein said flue- gas channel comprises a number of pipes that are arranged parallel and have a length of at least 5 m.

6. Cultivation system according to Claim 5, wherein said pipes discharge into a common water outlet and gas outlet.

7. Cultivation system according to any one of the preceding claims, wherein said connection between the separating tank and the water spraying system comprises a pump.

8. Cultivation system according to any one of the preceding claims, wherein said of water circulation means have both their inlet and their outlet in the said separating tank.

9. Cultivation system according to any one of the preceding claims, wherein a Venturi construction is used to provide pressure reduction in the water circulation means.

10. Cultivation system according to Claim 9, wherein the Venturi construction comprises a water inlet and a water outlet, separated by a constricted part.

1 1. Cultivation system according to Claim 10, wherein said constricted part comprises a gas inlet.

12. Cultivation system according to Claim 11 , wherein said gas inlet is connected to an air supply conduit.

13. Cultivation system according to any one of the preceding claims, wherein water turbulence generating means are connected to said separating tank.

14. Cultivation system according to any one of the preceding claims, comprising means for adding substances that bind contaminating gases are into said water.

15. Cultivation system according to any one of the preceding claims, wherein a number of separating tanks are connected in series.

16. Cultivation system according to any one of the preceding claims, wherein an electromagnetic device (85) is arranged in said return conduit (9), said electromagnetic device (85) comprises an induction coil (86) and a source of a variable-frequency voltage (87) for controlling said induction coil.