RU2385897C1 - Method of preparation of following and natural gases for usage in conventional engine - Google Patents

Abstract

FIELD: oil-and-gas production.

SUBSTANCE: method of preparation of following and natural gases for usage in conventional engine, consists in reduction of compounds concentration, allowing low detonation characteristic and increasing of probability of resin and carbon-black formation, is in that a prepared gas in mixture with oxygen-containing gas, for instance with air, is subject to thermal treatment at temperature from more than 450 up to 1100°C during 0.01-50 s at content of free oxygen in mixture (0.5÷5)%.

EFFECT: increasing of detonation characteristic of casing-head gas of petroleum production and raw natural gases and reduction of probability of resin and carbon-black formation at its burning, thanks to which mentioned gases are applicable for usage in the capacity of fuel for internal combustion engine practically without reduction of energy content.

14 cl, 1 dwg

Description

The invention relates to the oil and gas industry, in particular to the use of natural and associated gases in the energy sector.

When oil is extracted during the separation process, a large volume of associated hydrocarbon gases dissolved in it is formed, the output of which (gas factor) may exceed 100 m ³ per tonne of oil produced. They are a mixture of gaseous hydrocarbons of various molecular weights, including heavy ones. These associated gases, having a high energy content, are a valuable energy source. But they are practically not used for the production of heat and electricity for their own needs in the fields and adjacent regions and are still in large quantities flared in oil and gas production areas. For direct use in many types of modern power plants, in particular reciprocating internal combustion engines that drive small and medium power generators of local power plants, they are unsuitable due to the presence in them of a significant proportion of heavy C ₅₊ hydrocarbons having very low knock resistance and causing intense carbon and soot formation. This also applies to raw, that is, untreated, natural gases. As a result, the fields cannot use the associated or raw gases they produce for their own needs and are forced to use expensive imported fuel to burn them in flares. Further in the text of the description, the expression “associated and natural gases” will mean “associated and crude natural hydrocarbon gases”.

The reason for the use of associated and natural gases for reciprocating internal combustion engines is that the presence in the gas mixture is even insignificant, a little more than 1% vol. concentration of C ₅₊ hydrocarbons, can lead to the appearance of detonation in the engine and does not allow to reach its rated power. Knocking increases wear on engine parts and quickly disables it. Some types of power plants even provide for automatic shutdown when such gases are supplied to them. The detonation resistance of gas fuel for engines is quantified by the methane number - an analogue of the octane number for liquid fuel. The higher the methane number, the higher the knock resistance.

Two well-known methods for the preparation of associated and natural gases for use in internal combustion engines (hereinafter referred to as the preparation) are described below, based on various methods for separating individual fractions (See: Natural Gas and Condensate Processing Technology. Handbook. Part 1. M: Mineral , 2002, 517 pp.).

A known method for the preparation of associated and natural gases, which consists in their separation into fractions based on low-temperature processes using expansion refrigeration devices. At the same time, components reducing the methane number and causing intense gum and soot formation are removed from the feed gas. The method provides a high coefficient of extraction of the target components, as well as the efficient use of gas pressure and has received some distribution. However, the method requires the use of sophisticated cryogenic technology, high-speed turboexpander and metal-intensive heat-exchange equipment. Therefore, its use is justified only in the processing of large volumes of gas, at a level of 1 billion m ³ / year and above, and is economically unacceptable for the processing of gas volumes of 0.2–20 million m ³ / year, which are typical for small energy.

There is also a method of compression separation of heavy fractions of associated and natural gases, based on the compression and subsequent cooling of the gas in air and water coolers. At the same time, some of the heavy hydrocarbons and water vapors that make up the gas are condensed, and then separated in separators. As an independent, compression method is used extremely rarely and only for the separation of very "fatty", that is, containing many heavy components, gases. This method does not provide sufficient depth for the extraction of heavy components from the gas and is usually combined with other methods. In addition, it requires large amounts of energy for gas compression, expensive compressor equipment and a large volume of heat exchange equipment.

A common disadvantage of the described methods is their economic inefficiency in the processing of relatively small volumes of gases consumed by power plants with capacities from tens of kilowatts to several megawatts. Installations of exactly this power are required in most fields.

A known method for the preparation of associated and natural gases, using filtering the gas to be purified through filters from specially selected material (patent RU 2317844 from 03/27/2006). The method is implemented in an installation containing vertical and horizontal filters in the form of cylindrical housings having filter chambers with filter material deposited on a perforated frame, and the non-woven geotextile Geocom D-450 is used as filter material. The disadvantage of this method is the need for frequent changes of the filter cloth, too high a residual concentration of heavy hydrocarbons (0.6%) and a significant reduction in the energy content supplied to the gas installation due to the separated fractions.

Closest to the proposed technical essence and the achieved result is a method of preparing lean oil gases with a content of C ₃ H ₈ + higher from 50 to 100 g / m ³ by adsorption treatment. When implementing this method, the gas to be purified is driven through a solid porous material (adsorbent), which absorbs vapors and gases, mainly heavy hydrocarbons. The use of NaX zeolite is recommended as an adsorbent for the extraction of heavy hydrocarbons (С ₅ +) (See: Natural gas and condensate processing technology. Handbook. Part 1. M: Nedra, 2002, p.90). As hydrocarbons are absorbed, the adsorbent is gradually saturated with them, and the quality of purification deteriorates. To distill the absorbed hydrocarbons and restore the adsorption capacity, the adsorbent is treated with superheated water vapor. A mixture of water and hydrocarbon vapors, driven off from the adsorbent, cools and condenses. Molecular sieves and activated carbon are also used as adsorbent. The disadvantage of adsorption processes used for drying and cleaning is the frequency of their work associated with the need to change and regenerate the adsorbent, and the large physical volume of the equipment.

A common drawback of all known methods for the preparation of associated and natural gases is that they reduce the concentration of compounds having low methane numbers, separating heavy and light components and discarding components that are unsuitable for this type of engine, but nevertheless are valuable in energy terms. As a result, the total energy content of the prepared gas is reduced.

The objective of this proposal is to create an effective, cheap and compact way to prepare associated and natural gases for use in standard power plants based on reciprocating internal combustion engines, namely, to increase their detonation resistance and reduce the likelihood of tar and soot formation during their combustion. The method should maintain economic efficiency in the processing of relatively small volumes of gases.

The proposed method for the preparation of associated and natural gases for use in reciprocating internal combustion engines is that the gas being prepared in a mixture with an oxygen-containing gas, for example with air, is subjected to heat treatment at a temperature of (450 ÷ 1100) ° C for 0.01-50 s when the content of free oxygen in the mixture (0.5 ÷ 5)%.

In addition, heat treatment is carried out in several successive stages at different temperatures and oxygen concentrations at each stage.

In addition, heat treatment is carried out at a pressure above atmospheric.

In addition, the heating of the prepared gas or its mixture with oxygen-containing gas is carried out partially or completely due to the heat recovery of the treated gas.

In addition, the heating of the prepared gas or its mixture with oxygen-containing gas is carried out partially or completely due to the heat of the exhaust gases of the internal combustion engine.

In addition, the heat treatment temperature is controlled by changing the amount of oxygen-containing gas supplied.

In addition, the preparation of the mixture is carried out by injecting air or other oxygen-containing gas into the stream of the prepared gas.

In addition, additional reagents promoting the process, selected from the group, are introduced into the gas fed to the heat treatment: nitrogen oxides, hydrogen peroxide, halogen compounds, unsaturated or oxygen-containing hydrocarbons, or reducing the likelihood of soot formation (water vapor).

In addition, heat treatment is carried out in the presence of a catalyst.

In addition, the catalyst is selected from the group of catalysts for the oxidative condensation of methane: metal oxides Ca, Mg, Sr, Ba, Pb, Sn, Mn, Zn, V, Mo, W, rare-earth elements, or mixtures thereof, promoted by alkali metal oxides (Li, Na , K, Rb, Cs) and supported on oxide carriers - SiO ₂ , Al ₂ O ₃ , ZrO ₂ , MgO, TiO ₂ , aluminosilicates, zeolites).

In addition, the catalyst is selected from the group of catalysts for steam and / or carbon dioxide conversion of methane (massive, porous or supported on metal supports Ni, Co, Fe, Cr, Pt, and combinations thereof).

In addition, the catalyst is selected from the group of catalysts for the oxidative dehydrogenation of lower alkanes: simple and mixed oxides V, Sb, Mo, W, Nb, Ta, Te, Bi, Mg, Zn, Cu, Pb, Ni, Co, Fe.

In addition, heat treatment is carried out in the joint presence of catalysts of various groups.

In addition, the heat treatment is carried out in several successive stages, at each of which a catalyst is not used or catalysts of various groups are used.

Thanks to the heat treatment of the prepared gas in a mixture with a gas containing free oxygen, for example with air, the detonation resistance of the gas is increased, the likelihood of tar and soot formation is reduced, the gas becomes suitable for use as a fuel for piston internal combustion engines. This is achieved by reducing the concentration of compounds having low knock resistance and increasing the likelihood of gum and soot formation due to their selective conversion to compounds with higher knock resistance, not prone to gum and soot formation.

Due to the heat treatment of a mixture of the prepared gas with an oxygen-containing gas prepared in the indicated proportions, at the indicated temperature and time, the most complete selective conversion of compounds having low knock resistance and increasing the likelihood of tar and soot formation is ensured.

Due to the heat treatment in several successive stages at different temperatures and oxygen concentrations at each stage, the degree of conversion of compounds having low knock resistance and increasing the likelihood of tar and soot formation increases, and thereby the range of applicability of the method for associated and natural gases of very different compositions is expanded, which retains the high efficiency of the method.

Heat treatment at a mixture pressure above atmospheric speeds up the preparation process and reduces the dimensions of the installation.

Due to the fact that the heating of the prepared gas or its mixture with an oxygen-containing gas is carried out partially or completely due to the heat recovery of the treated gas, the energy consumption of the process is reduced.

Due to the fact that the heating of the prepared gas or its mixture with an oxygen-containing gas is carried out partially or completely due to the heat of the exhaust gases of the internal combustion engine, the energy consumption of the process is reduced.

Adjusting the temperature of the heat treatment by changing the volume of the supplied oxygen-containing gas simplifies the installation that implements the proposed method, facilitates process control and makes it more reliable.

The preparation of the mixture by injecting air or other oxygen-containing gas into the gas stream increases the degree of conversion of undesirable compounds by increasing the uniformity of the mixture and simplifies installation.

Introduction to the gas fed to the heat treatment of reagents selected from the group: nitrogen oxides, hydrogen peroxide, halogen compounds, unsaturated or oxygen-containing hydrocarbons promotes the process of selective conversion, allowing it to lower its temperature, and the introduction of water vapor reduces the likelihood of soot formation, that is, improves the quality of the product.

Carrying out heat treatment in the presence of a catalyst, accelerating the process and lowering its temperature, reduces energy consumption, reduces the dimensions of the installation that implements it, and also reduces the requirements for the applied structural materials, thereby reducing the cost of gas preparation.

The choice of catalyst from the three stated groups increases the degree of selective conversion of those types of gases that prevail in a particular raw or associated gas. The use of the most suitable catalyst deposited on a carrier that is most suitable for the design of the reactor, optimizing the process, reduces its cost.

Due to the fact that the heat treatment is carried out in the joint presence of catalysts of various groups, the degree of conversion of compounds having low detonation resistance and increasing the likelihood of gum and soot formation in cases where the prepared gas contains a mixture of several such compounds is increased, that is, the efficiency of the method is increased.

Due to the fact that the heat treatment is carried out in several successive stages, each of which does not use a catalyst or catalysts of various groups are used, at each stage the degree of conversion of hydrocarbon compounds having low knock resistance and increasing the likelihood of gum and soot formation increases, and thereby the range of applicability is expanded method for associated and natural gases of very different composition, which retains the high efficiency of the method.

The invention is illustrated in the drawing, which shows a block diagram of one of the possible installation options for implementing the proposed method.

The proposed method is as follows.

Associated or crude gas, prepared for use as fuel for a piston engine, is supplied through pipeline 1 (see drawing) for preheating to heat exchanger 2. Heated by the exhaust gases of engine 3, for which it is used as fuel. Next, the raw gas is finally heated to the heat treatment temperature in the recuperative heat exchanger 4 and enters the reactor 5. The heat treatment temperature lies in the range (450 ÷ 1100) ° C. At temperatures below 450 ° C, conversion does not occur, and this value is taken as the lower limit of the declared range. At temperatures above 1100 ° C, special measures are required to ensure the heat resistance of the equipment, especially resistant structural materials, which greatly increases the cost of installation. In addition, unwanted cracking of lighter hydrocarbons becomes noticeable. Therefore, the specified value is taken as the upper limit of the claimed range.

At the same time, it is fed into the reactor 5, preferably by injecting into the stream the supplied gas, oxygen, air or another mixture of gases containing free oxygen (hereinafter, oxygen-containing gas) in an amount in which the volume concentration of oxygen in the mixture with gas will be (0, 5 ÷ 5)%. The amount of incoming oxygen-containing gas is dosed by valve 6. This amount is small compared to the amount of gas being prepared, and therefore preheating of the oxygen-containing gas is not necessary. The declared limits were established experimentally and are justified by the following.

The presence of oxygen accelerates the thermal degradation of C ₅₊ hydrocarbons. In the absence or lack of oxygen, a significant part of these hydrocarbons turns into high molecular weight compounds (resin) and soot, deposited on the inner surface of the equipment and leading to its increased wear. At an oxygen concentration of 0.5%, the rate of deposition decreases sharply, while at a higher concentration, deposits are practically absent. At the same time, an increase in oxygen concentration leads to an increase in the proportion of gas oxidized to CO ₂ and, consequently, a higher loss of heat content of the fuel. In addition, when the oxygen concentration is above 5%, due to the high thermal effect of the reaction, the gas may heat up above the optimum temperature, and there may also be a danger of local formation of explosive mixtures, and therefore this value was set as the upper limit.

The residence time of the mixture of the prepared gas and oxygen-containing gas in the reactor, i.e. the heat treatment time, is (0.01 ÷ 50) seconds. At shorter times, the reaction does not have time to pass, and large ones require an unjustified increase in the size of the equipment.

Then, the heat-treated gas, in which the selective conversion of hydrocarbons with low detonation resistance occurred, enters the recuperative heat exchanger 4, where it gives part of its heat to the gas supplied to the preparation. The heat-treated prepared gas is finally cooled in an air cooler 7.

The quality of hydrocarbon gas preparation depends on the degree of homogeneity of its mixture with oxygen-containing gas. Therefore, it is preferable to supply an oxygen-containing gas by injecting it into a stream of hydrocarbon gas supplied to the reactor using the injector 8.

The gas consumption of the engine 3 changes with a change in the power taken from it. To stabilize the heat treatment, you can adjust the level of preheating of raw gas using a bypass valve 9, directing part of the exhaust gases to bypass the heat exchanger 2. You can also stabilize the temperature of the heat treatment by regulating the amount of oxygen-containing gas supplied to the reactor 5. To control the valves 6 and 9 serves as an automatic controller 10. The temperature and gas flow sensors included in the feedback system of the controller 10 are not shown in the drawing.

The presented block diagram of the installation implementing the proposed method is optimal, but not the only possible one. Installations without preheating of raw gas, with the preparation of the mixture before heating the components, without heat recovery of the treated gas are also functional.

The engine 3 is started on raw gas with an increased supply of oxygen-containing gas to the reactor 5. Since the heat exchangers and the engine usually warm up under part load, and the conversion process starts after only a few minutes, such a start does not harm the engine. If necessary, the installation can be supplemented with electric or flame starting heaters.

The proposed method can be carried out in several stages, when the processed gas is sequentially passed through several reactors, in each of which a certain heat treatment temperature and oxygen concentration are maintained.

The proposed method is feasible in the case when the pressure of the prepared gas is above atmospheric. In this case, the preparation process is accelerated, and the dimensions of the installation are reduced.

Significant acceleration of the preparation process is achieved when the heat treatment is carried out in the presence of catalysts. Depending on the composition of the gas being treated, one or another group of catalysts from the above ones is used, or several groups of catalysts at once, if the gas composition is unstable. The method of application of the catalysts — supported on the carriers, porous or massive — depends on the type of catalysts, their structural arrangement in the reactor, and the characteristics of the consumer of the prepared gas. The use of catalysts also simplifies the design of the installation, since in their absence thermal decomposition of C ₅₊ proceeds at significantly higher temperatures.

Different groups of catalysts are effective in the conversion of different groups of hydrocarbons. If the gas to be treated contains compounds of various groups, then the efficiency of the process is increased if catalysts of different groups are used together in reactor 5.

To increase the efficiency of the method, the conversion can be carried out in several successive stages, in which the gas passes from the reactor to the reactor, and in each reactor, catalysts of various groups are used or catalysts are not used. In this case, the temperature regime and oxygen concentration in different reactors can be set different in order to achieve the most complete conversion of all groups of hydrocarbon compounds included in the processed gas.

The introduction, along with air or an oxygen-containing gas, of additional reactants activating the process, for example, nitrogen oxides, hydrogen peroxide, halogen compounds, unsaturated or oxygen-containing hydrocarbons, facilitates and accelerates the thermal degradation of the components of the C ₅₊ fraction into the flow of gas supplied to the heat treatment gas. In addition, the introduction of these reagents, as well as water vapor, helps to reduce soot formation. But this improvement complicates the method and is advisable either when very large volumes of gas are processed and ease of installation is not of paramount importance, or when the content of the components of the C ₅₊ fraction in the feed gas is very high.

As it was established during the development of the proposed method, under these conditions, there is practically no conversion of lighter hydrocarbons C1 ÷ C4 having high methane numbers. At the same time, the conversion of C ₅₊ hydrocarbons having low octane numbers exceeds 95%. This means that the proposed method provides selective, that is, selective, conversion of components of natural or associated gas.

The main products of the selective conversion of C ₅₊ hydrocarbons during such heat treatment of associated gases under the conditions defined by us are (in decreasing order of yield) ethylene, methane, ethane and carbon monoxide. Other unsaturated and oxygen-containing compounds are also present in the products. All compounds formed have high methane numbers and are permissible in the composition of combustible gases for power plants of any type. The presence of oxygen-containing compounds in the fuel increases the completeness of its combustion and reduces the emission of harmful components with combustion products. In a number of countries, 2-2.5% oxygen-containing compounds (methanol, ethanol) are added to automotive fuels.

The proposed method allows simple and economical, without additional energy costs, the use of sophisticated equipment and with a slight loss of energy content of the feedstock, to convert at least 95% of C ₅₊ hydrocarbons into products more resistant to detonation, i.e. to increase the methane number of the gas supplied to the power plant, and, accordingly, its power, as well as reduce the likelihood of tar and soot formation and thereby increase the resource of its operation. The main advantage of the proposed method is that it allows the use of associated gases, which are still uselessly burned in most fields.

Claims (14)

1. A method of preparing associated and natural gases for use in reciprocating internal combustion engines, which consists in reducing the concentration of compounds having low knock resistance and increasing the likelihood of tar and soot formation, characterized in that the gas being prepared is mixed with an oxygen-containing gas, for example, air, subjected to heat treatment at a temperature of more than 450 to 1100 ° C for 0.01-50 s with a free oxygen content in the mixture of 0.5 ÷ 5%. 2. The method of preparing associated and natural gases according to claim 1, characterized in that the heat treatment is carried out in several successive stages at different temperatures and oxygen concentrations at each stage. 3. The method of preparing associated and natural gases according to claim 1, characterized in that the heat treatment is carried out at a pressure above atmospheric. 4. The method of preparing associated and natural gases according to claim 1, characterized in that the heating of the prepared gas or its mixture with oxygen-containing gas is carried out partially or completely due to the heat recovery of the treated gas. 5. The method of preparing associated and natural gases according to claim 1, characterized in that the heating of the prepared gas or its mixture with oxygen-containing gas is carried out partially or completely due to the heat of the exhaust gases of the internal combustion engine. 6. The method of preparation of associated and natural gases according to claim 1, characterized in that the heat treatment temperature is controlled by changing the volume of the oxygen-containing gas supplied. 7. The method of preparing associated and natural gases according to claim 1, characterized in that the preparation of the mixture is carried out by injecting oxygen-containing gas into the stream of the prepared gas. 8. The method of preparing associated and natural gases according to claim 1, characterized in that additional reactants promoting the process, selected from the group, are introduced into the gas supplied for heat treatment: nitrogen oxides, hydrogen peroxide, halogen compounds, unsaturated or oxygen-containing hydrocarbons, or reducing the likelihood of soot formation (water vapor). 9. The method of preparing associated and crude natural gases according to claim 1, characterized in that the heat treatment is carried out in the presence of a catalyst. 10. The method of preparing associated and crude natural gases according to claim 9, characterized in that the catalyst is selected from the group of catalysts for the oxidative condensation of methane: metal oxides Ca, Mg, Sr, Ba, Pb, Sn, Mn, Zn, V, Mo, W , rare earth elements, or mixtures thereof, promoted by alkali metal oxides (Li, Na, K, Rb, Cs) and supported on oxide supports — SiO ₂ , Al ₂ O ₃ , ZrO ₂ , MgO, TiO ₂ , aluminosilicates, zeolites. 11. The method of preparing associated and crude natural gases according to claim 9, characterized in that the catalyst is selected from the group of catalysts for steam and / or carbon dioxide conversion of methane (massive, porous or supported on metal supports Ni, Co, Fe, Cr, Pt and their combinations). 12. The method of preparing associated and crude natural gases according to claim 9, characterized in that the catalyst is selected from the group of catalysts for oxidative dehydrogenation of lower alkanes: simple and mixed oxides V, Sb, Mo, W, Nb, Ta, Te, Bi, Mg, Zn, Cu, Pb, Ni, Co, Fe. 13. The method of preparing associated and crude natural gases according to claim 9, characterized in that the heat treatment is carried out in the joint presence of catalysts of various groups. 14. The method of preparing associated and crude natural gases according to claim 9, characterized in that the heat treatment is carried out in several successive stages, at each of which a catalyst is not used or catalysts of various groups are used.