WO2011104464A1

WO2011104464A1 - Method for treating combustion fumes

Info

Publication number: WO2011104464A1
Application number: PCT/FR2011/050320
Authority: WO
Inventors: Alain Briglia
Original assignee: L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
Priority date: 2010-02-23
Filing date: 2011-02-15
Publication date: 2011-09-01
Also published as: FR2956592A1

Abstract

The invention relates to a method for treating combustion fumes, in which the fumes (1A) to be treated are conveyed to at least one treatment unit (2) and to at least one chimney (6) opening into the ambient air (6B). The invention is characterised in that the fumes are in fluid continuity with the ambient air via the chimney and in that the chimney is maintained in hydrostatic equilibrium, so as to prevent the fumes from escaping through the chimney and the ambient air from reaching the treatment unit by passing through said chimney.

Description

Process for treating fumes from combustion

The invention relates to a method for treating fumes from combustion.

It relates more particularly to processes where fumes produced by at least one combustion unit are normally conducted through a piping system, or to a treatment unit, for example a CO ₂ capture unit (carbon dioxide) contained in the fumes, either to at least one exhaust stack, or to both. This can happen in case of voluntary shutdown or failure of the flue gas treatment unit, while the combustion unit, for example a boiler intended to produce energy, continues to operate.

Depending on the combustion unit, the flue gas flow can reach very high values. A technical problem that arises in all cases is to control the flow to the treatment unit or to the chimney, in particular during the transient phases, for example during the period following a stop or start of the unit. treatment, or following a significant change in the flow rate admitted by the treatment unit.

This problem is conventionally solved using valves. For example, it is possible to use an isolation valve for the exhaust stack and possibly another for the treatment unit. These two valves can be combined into a three-way valve. When the flue gas treatment unit comes to a standstill, access to the flue gas chimney is opened and, if necessary, access to the treatment unit is closed. Conversely, when the treatment unit starts, while the smoke is discharged through the chimney, access to the chimney is closed and access to the treatment unit is opened.

Unfortunately, these openings or closures of valves take some time, especially for large diameter valves. In addition, these openings or closures are not necessarily ideally synchronized. This can create significant disturbances in the flue gas flow, including an overpressure at the outlet of the combustion unit. At this overpressure is associated a risk that the combustion unit stops, certain safety thresholds having been crossed.

The problem to be solved is therefore to reduce the risk of stopping a combustion unit when it is discharging either into a flue gas treatment unit, or into a flue and flue gas flow to said unit. treatment undergoes significant change, for example following a stop or start of the processing unit.

To this end, the solution of the invention relates to a method for treating flue gases from combustion, in which:

said fumes to be treated are fed either to at least one treatment unit, or to at least one chimney opening into the ambient air, said fumes being in fluid continuity with the ambient air via said chimney; and

- Keeping said chimney in hydrostatic equilibrium, so as to prevent, on the one hand, said smoke out through said chimney and, on the other hand, the ambient air to reach said treatment unit through said chimney;

a given flow rate of fumes to be treated is injected into said treatment unit; and

when said stack has a hydrostatic pressure difference between its internal base and the ambient air at a reference point, said determined flow rate of fumes to be treated injected into said treatment unit is regulated so as to maintain said pressure difference at setpoint.

The fumes in question come from a combustion, that is to say for example from a boiler burning one or more fuels with as air oxidizer and / or mixtures richer in oxygen than air . In a particular case, the oxidant (s) are pure oxygen at least 99% by volume. The fumes to be treated are at least a part of the fumes generated by the combustion. Some of the fumes generated may be recycled or not treated, or treated in another treatment unit. Combustion can also occur in a gas turbine. It can happen in an industrial oven. It can happen in a chemical plant, steel or a cement plant.

The flue gas treatment unit can perform a unit operation, such as drying, compression or desulphurization, or perform several operations, for example those typically associated with the capture of CO ₂ (in particular: drying, compression, purification of CO ₂ by different technologies, especially cryogenic distillation). In general, the fumes are conducted by a piping system which includes pipes or carnots. The hydraulic diameter of these elements can go up to a few meters in the case of a power station. The piping system may comprise intermediate elements, for example valves, flow meters, or elements of physical or chemical treatment of the fumes. It can be formed of elements in series or in parallel in the direction of the fluid flow, or have a more complex structure. The composition and parameters of the fumes may have changed between the combustion and the flue gas treatment unit. The chimney is suitable for the evacuation of the fumes to be treated, especially when they are not, or not entirely, treated in the treatment unit.

The fumes to be treated are conducted through the piping system to at least one treatment unit. The fumes are also conducted to at least one chimney capable of allowing the evacuation of all or part of the fumes produced by the combustion. The piping system generally includes a bypass for conducting the flue gas to at least one chimney. In the case of power plants, the height of these chimneys can be up to several hundred meters. This injection is generally carried out by means of a compression means, of the fan or compressor type.

The fumes to be treated are prevented from flowing through the chimney. In a "normal" operating state, all the fumes to be treated are effectively treated and are not sent to the chimney.

The fumes are in fluid continuity with the ambient air via the chimney. There is no material obstacle to the flow through the chimney. The part of the pipe system leading to the chimney is open. In particular, it is not closed by a valve. There may be valves, but these are busy, i.e. not closed. This means that if the fumes were pushed to the chimney, they could flow through this chimney.

The fumes to be treated are prevented from flowing through the chimney while maintaining a sufficient hydrostatic equilibrium in this chimney. Similarly, the ambient air is prevented from reaching the piping system via the chimney. The latter has a certain vertical extension and the column of fluid that it contains is subjected to gravity, to the pressure forces at the top and to the base of the chimney, as well as to wall friction and viscosity. case of movement. The hydrostatic equilibrium need not be perfect, that is to say that it does not aim at the absolute immobility of the internal atmosphere of the chimney. We consider that we are at a sufficient hydrostatic equilibrium when there is no significant movement of the fluid in the chimney. A movement is significant if it corresponds to a smoke outlet from the chimney or to an ambient air inlet in the piping system via the chimney.

An advantage of the hydrostatic equilibrium blocking of the valve-type hardware element blockage is that the balance can be broken without the need to remove the material cause of the blockage. Thus, if the flue gas treatment unit stops or goes down as a result of a voluntary decision or a failure, the accumulation of fumes in the piping system will break the hydrostatic equilibrium without creation of significant overpressure in the piping system. In particular, it will not be necessary to open valves. The pressure to break the hydrostatic equilibrium of the fluid column is much lower than that created by the slow opening, possibly poorly synchronized, of a valve system. It is understood that the risk that stopping or lowering of the flue gas treatment unit causes an untimely stop combustion is then greatly reduced or canceled.

If the treatment unit stops or falls, the hydrostatic equilibrium ruptures and the fumes will enter the chimney and evacuate. The phenomenon then amplifies itself by pulling. Conversely, fumes evacuating via the chimney, restarting or ramping up the flue gas treatment unit can restore a hydrostatic balance in the chimney. There is no need to close a valve. It is then necessary to first overcome the forces due to the draw, the fluid column in the chimney being hot, and establish a mechanical balance. Then, once the column of fluid in the chimney is cooled, a thermal equilibrium has been created, it is brought back to the "normal" situation described above.

Moreover, according to particular embodiments, the invention may comprise one or more of the following characteristics: an interface between said fumes to be treated and the ambient air having been established in said stack, said setpoint value being chosen so that said interface is substantially halfway up said chimney. one or more gaseous compositions are evaluated at one or more locations chosen from the following possibilities: at different heights of said chimney and / or at points situated in said fumes to be treated between said combustion and said treatment unit and / or between said combustion and said chimney. said fumes are produced by combustion with oxygen and said treatment unit is a unit for purifying the carbon dioxide contained in said fumes.

The injection of the fumes to be treated in the treatment unit is generally carried out by means of a compression means, of the fan or compressor type.

The chimney at all times has a difference in hydrostatic pressure, positive or negative, between its base, ie where the fumes are potentially admitted into the chimney, and a hydrostatic pressure reference point. This reference point must be such that the pressure measured at this point is independent of the composition and condition of the fluid column in the chimney. This may be for example a point located outside the chimney, at its base, and subjected to the pressure of Γ ambient air.

This difference in pressure of the stack can be regulated by acting on the flow rate of fumes to be treated admitted into the treatment unit. Indeed, the higher the flow rate, the lower the flue gas pressure in the piping system, especially at the base of the chimney; the difference in hydrostatic pressure of the chimney is lower, which tends to allow air to enter the chimney. Conversely, the lower the injected flow rate, the higher the pressure rises at the base of the chimney, the higher the hydrostatic pressure difference of the chimney, which tends to raise the column of fluid in the chimney, it is to make it penetrate fumes.

In practice, when the chimney is substantially at the hydrostatic equilibrium, a gaseous interface between the ambient air and the fumes comprising a large amount of C0 ₂ and water is established at a certain height in the chimney. This height conditions the weight of the fluid column in the chimney, the air and fumes having a priori not the same density. By regulating the hydrostatic pressure difference to a certain setpoint, it is possible to choose how high the interface is established. The setpoint takes into account, in particular, the composition and the temperature of the fumes and can therefore vary with time. The method may include measuring or evaluating gaseous compositions to at least determine whether there is air or smoke. Thus, it is easier to control the position of the air / flue interface in the chimney or between the combustion and the treatment unit and / or the chimney. By purification of the carbon dioxide contained in the fumes, it is meant that the treatment unit is able and intended to remove certain other bodies or compounds, so as to obtain a more concentrated fluid C0 ₂ that the fumes to be treated injected into the processing unit.

The invention also relates to a combustion and flue gas treatment plant comprising at least:

- At least one unit adapted to and designed to perform a combustion producing fumes and at least one treatment unit adapted to and designed to treat said fumes; and

- A piping system comprising a portion adapted to and adapted to conduct said fumes to be treated to said treatment unit and another portion adapted to and adapted to conduct said fumes to be treated to at least one chimney surrounded by the ambient air;

characterized in that it further comprises means for maintaining a hydrostatic equilibrium in said chimney, said part adapted to and designed to drive said fumes to be treated towards said chimney being open, so as to avoid, on the one hand, that said fumes to be treated do not exit through said chimney and, secondly, that said ambient air does not enter said portion of said piping system adapted to and designed to drive said fumes to be treated to said treatment unit.

Furthermore, according to particular embodiments, the invention may comprise one or more of the following characteristics: said chimney, comprising an internal base, said means for maintaining a hydrostatic equilibrium in said chimney comprise a compression means for injecting said fumes into said treatment unit with a given flow rate and a system for controlling said determined flow rate at the pressure difference between a point in said internal base of the stack and a reference point in said ambient air. the plant further comprises means adapted to and designed to evaluate one or more gaseous compositions at one or more locations selected from the following possibilities: at different heights of said stack and / or at points of said piping system. said unit adapted for and designed for combustion is connected to at least one oxygen-rich gas source suitable and intended to serve as an oxidizer for said combustion and said processing unit adapted to and designed to treat said fumes is a unit for purifying the carbon dioxide contained in said fumes. The compression means is generally a fan, a compressor or a system consisting of fans and / or compressors. It must be able to modify the hydrostatic pressure in the piping system, especially at the base of the flue gas chimney. The purpose of measuring or evaluating one or more gaseous concentrations in the piping system and / or the chimney is to be able to discriminate between air and smoke and thus to detect the position of the air / flue gas interface.

Other particularities and advantages will appear on reading the description below, made with reference to the figures, among which:

Figure 1 shows a combustion device and flue gas treatment according to the state of the art;

FIG. 2 represents an example of a combustion and flue gas treatment device according to the invention.

In Figure 1, there is shown a plant producing energy. It comprises a boiler 1 which burns fuel and produces fumes 1a, and a unit 2 for treating fumes. This unit 2 is designed to purify the C0 ₂ contained in the flue gas. A fan 3, pressure-controlled by a system 3a controls the pressure in the combustion chamber of the boiler 1. Fans 4 and 5, controlled in flow, allow the possible recycling of fumes in the boiler 1. A system of Pipelines 1b, 1a, 1d lead the flue gas to either the treatment unit 2 or to a chimney 6 for evacuation. More specifically, the part lb, the duct system leads to the unit 2. A bypass ld leads to the chimney 6. It is provided with an isolation valve 7. The branch that leads to the unit 2 has an isolation valve 8.

In normal operation, the compressor 10 injects the fumes to be treated in the unit 2. It is controlled by a system 10a as a function of the upstream pressure. The valve 7 is closed, so that the chimney 6 does not receive smoke la. Valve 8 is open.

In case of shutdown of the flue gas treatment unit 2, possibly due to a shutdown of the compressor 10, valve 8 is closed and valve 7 is simultaneously opened. opening time, the pressure rises at point 9 and in the piping system upstream of point 9, which can cause the boiler 1 to shut down.

Conversely, at the restart of the unit 2, while the fumes are discharged through the chimney 6, the valve 8 is opened and the valve 7 is closed. The same problem may arise.

In Figure 2, the compressor 10 comprises a servo system 10a the hydrostatic pressure difference between a point 10c located in the base 6d of the chimney 6 and a reference point 10b located outside the chimney. Thus, the part ld of the pipe system leading to the chimney remaining open (not closed by a valve 7), it is possible to regulate the hydrostatic pressure difference seen by the stack 6 by varying the flow rate injected by the compressor 10 in the flue gas treatment unit 2, so that the ambient air 6b does not enter the pipe system 1b, 1a, 1d and the flue gas does not exit through the chimney 6.

A gas interface 6c is formed in the chimney between the ambient air 6b and the fumes 1a. By regulating the hydrostatic pressure difference of the chimney 6, the interface 6c can be raised or lowered. In practice, it is preferably stabilized at half height of the chimney 6, so as to minimize the gas inlet-outlets via the chimney 6.

In a complementary manner, it is possible to place systems 11 for evaluating the C0 ₂ concentration at different heights of the stack 6, so as to locate the interface 6c and to correct the hydrostatic pressure difference set point of the stack 6. A smaller difference lowers the interface 6c, while a stronger difference makes it go up.

The installation may also include means 12 for evaluating the gaseous composition in the parts 1b, 1a and / or 1d of the pipe system, for detecting an ambient air inlet 6b.

In case of shutdown or deceleration of unit 2, the hydrostatic equilibrium of the chimney 6 is broken and the overflow of fumes can flow through the chimney 6 without the appearance of a significant overpressure upstream. . Combustion unit 1 is therefore protected when all or part of the smoke must be evacuated without treatment.

Claims

claims

Process for the treatment of fumes (la) resulting from a combustion (1), in which: said fumes (la) to be treated are fed to at least one treatment unit (2) or to at least one stack ( 6) opening into the ambient air (6b), said fumes (la) being in fluid continuity with the ambient air (6b) via said chimney (6),

said chimney (6) is maintained in a hydrostatic equilibrium, so as to prevent, on the one hand, said flue gases (la) from exiting through said chimney (6) and, on the other hand, the ambient air (6b) from reaching said processing unit (2) through said stack (6);

a given flow rate of fumes (la) to be treated is injected into said treatment unit (2); and

when said stack (6) has a hydrostatic pressure difference between its internal base (10c) and the ambient air (6b) at a reference point (10b), said determined flue gas flow (1a) to be treated is controlled said processing unit (2) so as to maintain said pressure difference at a set point.

A method according to claim 1, characterized in that an interface (6c) between said fumes (1a) to be treated and the ambient air (6b) is established in said stack (6), said setpoint value of so that said interface (6c) is substantially halfway up the chimney (6).

Process according to either of Claims 1 and 2, characterized in that one or more gaseous compositions are evaluated at one or more locations (9, 10b, 10c, 1c) chosen from the following possibilities: at different heights of said stack (6) and / or at points located in said fumes (la) to be treated between said combustion (1) and said treatment unit (2) and / or between said combustion (1) and said chimney (6).

Process according to any one of Claims 1 to 3, characterized in that the said fumes (la) are produced by combustion (1) with oxygen and the said treatment unit (2) is a unit for purifying the dioxide of carbon contained in said fumes (la).

5. Combustion and flue gas treatment plant (la) comprising at least at least one unit (1) adapted to and designed to perform a flue-producing combustion (1a) and at least one treatment unit (2) adapted for and designed to treat said flue gas (1a); and

a piping system (lb, le, ld) comprising a part (1b, 1c) suitable for and designed to conduct said fumes (1a) to be treated to said treatment unit (2) and another part (1d) suitable for and adapted to conduct said fumes (1a) to be treated to at least one stack (6) surrounded by the ambient air (6b);

characterized in that it further comprises means (10, 10a) for maintaining a hydrostatic equilibrium in said stack (6), said part (1d) adapted to and designed to drive said fumes (1a) to be treated to said chimney (6) being open, so as to prevent, on the one hand, that said fumes (la) to be treated do not exit through said chimney (6) and, on the other hand, that said ambient air (6b) does not enter said portion (1b, 1c) of said piping system (lb, 1c, 1d) adapted to and adapted to conduct said flue gas (1a) to be treated to said treatment unit (2); said chimney (6) having an internal base (6d), said means (10, 10a) for maintaining a hydrostatic equilibrium in said chimney (6) comprise a compression means (10) for injecting said fumes (1a) in said processing unit (2) with a determined flow rate and a system (10a) for controlling said determined flow rate at the pressure difference between a point (10c) in said internal base (6d) of the stack (6) and a reference point (10b) located in said ambient air (6b).

Installation according to claim 5, characterized in that it further comprises means (11, 12) adapted to and designed to evaluate one or more gaseous compositions at one or more locations (9, 10b, 10c, 1c) chosen from following possibilities: at different heights of said chimney (6) and / or at points of said piping system (lb, le, ld).

Installation according to any one of claims 5 or 6, characterized in that said unit (1) adapted to and designed to achieve combustion is connected to at least one oxygen-rich gas source suitable and intended to serve as an oxidizer for said combustion and that said processing unit (2) adapted to and designed to treat said fumes (la) is a unit for purifying the carbon dioxide contained in said fumes (la).