Patent Application
20130143170
The invention relates to a contrivance designed as crude gas bleeder/flare with variable bleeder/flare crude gas outlet consisting of several tubes nested inwardly which form a bleeder/flare for bleeding off/flaring crude gases, this arrangement containing a nozzle of a variable cross-section, said nozzle controlling the feed of crude gas in such a manner that an almost constant velocity can be adjusted at the bleeder/flare outlet side and an almost constant pressure be adjusted on the bleeder/flare inlet side. In this way undesired extinction and straying of the bleeder/flare flame can be avoided during operation. The invention also relates to a process for the combustion of coke oven crude gases, in which a constant flow velocity is achieved at the discharge side of the bleeder/flare by the use of a nozzle of a variable cross-section and the use of tubes of a specific cross-section ratio.
Many industrial processes produce gases which are not used for further applications because this is not desired for economical or technical reasons. Examples of such processes are the production of coke oven gas or the production of refinery products, with waste gases being obtained which are destroyed by combustion or burning. This process is also called bleeding-off/flaring because the combustion process is normally run at the outlet end of an open tube and is not used for the generation of energy. The gases to be bled off/flared are typically obtained at too high or varying pressure during a malfunction in the gas-treating or gas-purifying plant section and can therefore not be used for further applications.
It is also possible that the gases intended for combustion are of a chemical composition which results in a lower calorific value and, therefore, the gases can only be used to a limited extent for further applications. Due to these reasons the intended bleeding-off/flaring of the gases also encounters further technical problems. For bleeding-off/flaring, the gas to be bled off/flared must be supplied at a sufficient and constant pressure to ensure adequate combustion. Because the combustion gases are normally discharged into the surrounding atmosphere the gas to be bled off/flared must be combusted as completely as possible and without any interruption. This means that not only the pressure of the gas to be bled off/flared must be controlled but also the air supply for combustion. In addition, it must also be ensured that the escaping gas can immediately be re-ignited at the discharge end of the bleeder tube when the flame goes out, this requiring the availability of a reliable ignition device.
Finally, efforts are made to avoid so-called “straying” of the flame or at least to reduce it significantly. This process denotes the uncontrolled flickering of the flame at the outlet end of the tube, in particular under the influence of wind. This straying causes a shift of the point of maximum heat flux intensity of the flame in such a way that the bleeder/flare facilities or even adjacent plant sections may be damaged.
Contrivances, suitable for bleeding off/flaring a gas to be combusted and designed for avoiding such problems, are known in prior art. U.S. Pat. No. 5,472,340 A describes a contrivance which claims a flare igniter and a crude gas flare intended for this purpose. The contrivance includes at least two conduits which are of different length and share a common longitudinal axis, the conduits being arranged as an outer and inner conduit at least in sections in such a manner that air for combustion can pass into the area disposed between both conduits, and in which one end of the inner conduit allows the entry of combustion gas in such a way that the contrivance forms a flare. At least two points of the flare also comprise fins for the deflection of the gas and air flows during combustion. Optionally the ignition device can also be operated using a solar powered source.
The said invention particularly solves the task of providing a reliable flare igniter. However, the contrivance mentioned can only be operated without any interruption at a relatively constant pressure of the gas to be combusted. No process step is mentioned which allows bleeding off/flaring the gas also at a low pressure. Also, no process step is mentioned for lessening the influence of wind and ensuring atmosphere-independent, undisturbed combustion. Finally, when combusting high-carbon gases efforts are made to minimise the formation of soot in order to exclude detrimental impact on the surrounding atmosphere. Again, for this measure no process step is mentioned in the said patent application. Finally, the contrivance can also be damaged by an excessive thermal load as taking place, for example, in a straying flame direction.
Therefore, the objective is to provide a contrivance which allows/obtains an as complete as possible and soot-free combustion of the gas to be bled off/flared, with the lowest possible emission of soot and nitrogen oxides. The combustion should also take place in an undisturbed and uninterrupted manner at varying inlet pressures of the gas to be bled off/flared. The flame direction should be as constant as possible to maintain a low thermal load of the bleeder/flare material. The impact of wind on the flame should have no disturbing influence. Finally, the contrivance should also provide a reliable ignition of the gas to be bled off/flared.
The invention achieves the objective by a contrivance of a variable opening cross-section for bleeding off/flaring combustible gases, the said contrivance consisting of three different tubes arranged around a common longitudinal axis, and the tubes being arranged at least in sections at a common cross-section level, and the inner tube being designed as a gas feed tube, and this tube being equipped with a baffle of variable cross-section at the opening that ends upwards in vertical direction, said baffle being used to close or control the gas flow and being equipped with an automatable mechanism for adjusting the opening cross-section. The contrivance typically also consists of at least one air guide plate and shaped sections at the outer tube which allow a directed supply of air and an undisturbed burning of the gas to be bled off/flared.
The contrivance also includes an ignition device which allows the undisturbed ignition of the gas as well as feed devices for an inert fluid which is preferably water vapour in order to minimise the formation of soot and carbon monoxide, i.e. to combust the hydrocarbonaceous gas as completely as possible. The inlet pressure of the escaping gas and its discharge velocity can be controlled in a wide range or kept constant by the baffle of variable cross-section. As a result, combustion and flame formation can be maximally controlled and optimised.
In particular, the invention claims a contrivance of a variable opening cross-section for bleeding off/flaring combustible gases, consisting of
and which is characterised in that
The embodiment of the tubes can also be of any type. Typically, the outer tube, also called mixing tube, is provided at the top with an extension that enlarges upwards. It is also called diffuser. Said upper part is used for directing the flame. The lower part of the mixing tube is primarily used for supplying air. This part of the mixing tube is also called confuser and enlarges into a downward opening. Said part can also be provided with baffle plates or air guide plates for the directed supply of combustion air. In principle, baffle plates or air guide plate can be provided at each tube and in any arrangement. Embodiments for the design of the tubes are known in prior art.
The combustion air enters the mixing tube through the confuser and is routed both into the area between the mixing tube and the inner tube as well as between the inner tube and the gas feed tube. This results in a two-stage combustion which counteracts the formation of nitric oxides.
The baffle, which adjusts or closes the cross-section of the inner tube, can be of any type, provided it reliably controls or closes the cross-section of the inner bleeder/flare tube. The diaphragm is preferably made of a heat-resistant material in order to be resistant to the temperatures of the flame forming at the bleeder/flare outlet. The baffle material must also be resistant to any corrosive constituents contained in the gas to be bled off/flared. This material is preferably heat and corrosion resistant steel.
In an exemplary embodiment, the baffle consists of plates which are closable concentrically, tangentially and circularly towards the gas feed tube centre. This corresponds to an embodiment as it comparatively exists in a photographic diaphragm. For opening and closing these plates are moved in horizontal direction towards the centre of the tube. The number and size of the plates can be optional. It is important that the material of the baffle is resistant to the prevailing temperatures and to the gas or liquid constituents. An embodiment of baffles which close tangentially and circularly towards a tube centre (“iris shutters”) is known from U.S. Pat. No. 4,094,492A. However, this patent specification does not teach any control of bleeders/flares for the combustion of gases, including the resulting special requirements, such as high temperatures and resistance to corrosive gases.
In a further exemplary embodiment, the baffle consists of plates which are closable concentrically, secantially and directly horizontally towards the gas feed tube centre.
In a further embodiment, the plates can be tilted upwards or downwards in vertical direction for opening. In this case, the plates are designed as blades which are preferably drawn upwards in flow direction by an actuator. This corresponds to an embodiment as it comparatively exists in an iris diaphragm. The more the blades are pulled upwards, the more the diaphragm opens. The number of blades, their size and material can also be optional. An embodiment of baffles which are drawn upwards or downwards in the tube in vertical direction for opening (“iris nozzles”) are known from DE 10002529 A1. This patent specification neither teaches any control of bleeders/flares for the combustion of gases, including the resulting special requirements, such as high temperatures and resistance to corrosive gases.
In an exemplary mode, the diaphragm can be adjusted by an electric actuator. However, a pneumatic actuator can also be selected. The selection of the actuator type is left to the executing person skilled in the art. The arrangement of the baffles can temporarily or permanently be selected in such a manner that there is an aperture in the centre of the baffle arrangement.
In an embodiment of the invention, at at least one point inside the gas feed tube, the inner tube or the mixing tube a nozzle is located for feeding an inert gas. Typically, this is water vapour. Depending on the combustion conditions the feeding of water vapour as driving gas enables continuous flame control and a considerable reduction in the formation of soot and carbon monoxide at almost complete to complete combustion of the hydrocarbons contained in the gas. This contrivance can be a nozzle or a simple inlet tube. Nozzles for feeding water vapour into gases to be bled off/flared are known in prior art. An exemplary embodiment of feed nozzles is taught in DE 69917073 T2. These nozzles can in turn be provided with a controlling device of any type. The latter can also consist of baffles like the inventive contrivance.
In a further embodiment of the invention, the inventive contrivance is provided with a device for igniting the gas. For example, it is thus possible to arrange ignition lances inside the cross-section of the inner tube or the mixing tube. In an advantageous embodiment these are at least two ignition lances which are arranged at an angle of 80° to 100° and with the aid of which an electric arc or ignition spark can be generated by electric voltage. The electric voltage can be generated by any means. It can be freely selected to ensure reliable ignition. An example of a prior-art ignitor rod arrangement is given in U.S. Pat. No. 4,147,498A.
The gas inlet/gas feeder to the bleeder/flare can also be of any type. In a simple embodiment this is a simple tube leading into the gas inlet of the inner tube in such a way that the pressure of the escaping gas is controlled by the inventive baffle only. In a further and preferred embodiment a bleeder/flare valve, which can be shut off, is located below the inner tube and the mixing tube. This bleeder/flare valve can be of any type. For example, it can consist of a float cup with water supply so that the pressure of the gas fed into the float cup can already be controlled to some extent or shut off at the gas inlet to the bleeder/flare. An embodiment of a pressure-controlling float cup is described in EP 1390440 B1.
In a further embodiment, the bleeder/flare valve comprises at least a float cup consisting of two compartments, with said compartments to be opened, controlled and closed independently of each other. In this way the bleeder/flare valve is of redundant configuration as a result of which the bleeder/flare valve is still operable even in the case of a failure of one compartment and the gas to be bled off is prevented from being discharged into the atmosphere in an unburned state. Gas feeding bleeder/flare valves provided with float cups are sufficiently known in prior art. Preferably, the bleeder/flare valves are opened, controlled or closed pneumatically with the aid of a pneumatic cylinder. For the embodiment of the present invention it is possible to actuate each compartment individually. As two pneumatic cylinders are available the float cup is still operable even in the case of a failure of one cylinder.
The invention also claims a process for the combustion of coke oven crude gas using the inventive contrivance. It typically feeds the gas to be bled off/flared into the gas feed tube and controls the setting of the discharge velocity of the gas to be bled off/flared by means of the baffle of variable cross-section. Typically, the velocity of the escaping gas to be bled off/flared is controlled during bleeding off/flaring in such a manner that the velocity remains constant and an undisturbed flame control is ensured. This procedure also prevents the undesired straying or extinction of the flame.
In an embodiment of the invention, a two-stage combustion leads to a reduced flame temperature. This two-stage combustion is achieved by selecting the ratios of the cross-sections of gas feed tube and inner tube as well as of inner tube and mixing tube in such a way that a reduced air feed rate to the inner tube leads to a substoichiometric combustion air ratio (first combustion stage) and the proportionately increased air feed rate via the annular gap between the mixing tube and the inner tube to the upper part of the mixing tube leads to a hyperstoichiometric combustion air ratio in the mixing tube above the inner tube (second combustion stage). This two-stage combustion counteracts the formation of nitrogen oxides.
In a further embodiment of the invention, an inert gas is fed into the gas feed tube, the inner tube or the mixing tube. Preferably, this inert gas is water vapour. However, additional crude gas, intended for bleeding off/flaring, can be supplied. Finally, in a further embodiment of the invention, a mixture of water vapour and gas to be bled off/flared can also be supplied. This mixture is preferably supplied at a pressure of 7 to 15 bar.
Suited for bleeding off/flaring are all gases of a sufficiently high calorific value. Typically, these gases are coke oven crude gases or refinery gases.
The feeding of the gas to be bled off/flared into the inventive bleeder/flare can be performed as desired. In a simple embodiment, this can be performed by a simple tube in an uncontrolled manner. In a preferred embodiment, an upstream bleeder/flare valve comprising at least a float cup is arranged below the bleeder tubes.
As described, this valve is preferably made of two float cups which may also be designed as two compartments to be operated independently. In a preferred embodiment, each of the two compartments of the float cup of the upstream bleeder/flare valve can synchronously be opened, controlled or closed by a pneumatic cylinder.
However, each compartment of the entire float cup can be operated individually. In this way, an undesired blockage of the valve can be counteracted in the case of a failure of a controlling device to prevent the gas from being discharged into the atmosphere in unburned state. According to the invention, a gas collecting vessel/receiver serving as a buffer vessel can be allocated to the bleeder/flare in order to counteract a pressure build-up when closing the baffle or the upstream bleeder/flare valve.
Finally, the use of the inventive process allows a considerable reduction of the number of crude gas bleeders/flares since the heat development of the bleeders/flares is lower and the reliability higher. Half the normal number of bleeders/flares is frequently sufficient. The bleeders/flares can also be of lower height design since heat radiation is lower and the emission of unburned gas does not have to be taken into account.
The invention has the following advantages: The bleeder/flare can be operated at a constant discharge velocity of the gas to be bled off/flared, resulting in continuous flame control accompanied by a high bleeding-off/flaring reliability. Straying flames accompanied by an undesired shift of the point of maximum heat flux intensity are avoided in order to prevent any damage to the bleeder/flare and impairment of the environment. The impact of wind results in a considerably lower disturbing influence on the bleeding-off/flaring process than in prior-art devices. The possibility of installing a reliable ignition device ensures continuous combustion in such a way that the undesired emission of non-burned gas is practically suppressed. The formation of soot when bleeding off/flaring high-carbon gas can practically be excluded by feeding inert gas and the formation of nitrogen oxides can successfully be counteracted by two-stage combustion.
The invention is illustrated in more detail by means of four drawings showing exemplary embodiments, the invention not being limited to these embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2010 035 153.9 | Aug 2010 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2011/004111 | 8/16/2011 | WO | 00 | 2/20/2013 |
