Autothermal reforming process of hydrocarbon supply source containing higher hydrocarbon

Method for autothermal conversion of hydrocarbon feed containing higher hydrocarbons

The present invention relates to soot-free autothermal conversion (ATR) of hydrocarbon feeds containing higher hydrocarbons.

In autothermal conversion, the combustion of the hydrocarbon feed is carried out in the combustion zone of the furnace by a pyrotechnic reaction with a substoichiometric amount of oxygen, and then the partially combusted feed is vaporized in a fixed bed of a vapor reforming catalyst. Substoichiometric combustion of hydrocarbons results in the formation of harmful soot. By using a dedicated burner design and by controlling the operating conditions of the ATR method, soot formation can be overcome. Soot is formed in the flame of the autothermal reactor within a certain range of operating conditions. When the amount of vapor relative to the other components fed into the ATR reactor is below the critical value, soot is formed in the feed to the reaction. One such burner for ATR is described in U.S. Patent 5,496,170. The limiting amount of steam can be expressed as the critical ratio of steam to carbon, which is the ratio of the molar feed flow rate of steam to the molar flow rate of carbon in the hydrocarbon feed. The hydrocarbon feedstock may be in the form of natural gas or hydrocarbons including LPG, butane, naphtha and the like. The molar flow rate of carbon is calculated by multiplying the molar flow rate of the hydrocarbon by the carbon content of the hydrocarbon.

Examples of operating conditions that do not cause soot formation have been summarized in the paper by Christensen and Primdahl (Hydrocarbon Processing, March 1994, pages 39-46). These conditions are shown in Table 1. These tests were carried out in a pilot plant. Due to the relatively small heat loss from the pilot plant, the adiabatic ATR outlet temperature will be higher than the measured ATR outlet temperature. This means that if a large device (from which the heat loss is small) is subjected to strictly the same operating conditions, the ATR outlet temperature will be close to the adiabatic ATR outlet temperature. The soot precursor is formed in the combustion section of the ATR. Most of the heat loss occurs after the combustion zone. The subsequent heat loss will not have any effect on the reactants in the combustion zone. The oxygen to carbon ratio (O2/C) is also shown in Table 1. The definition of this ratio is similar to the ratio of steam to carbon, but with oxygen instead of steam. The outlet temperature of the ATR reactor can be calculated from the O2/C ratio, when the heat loss from the reactor is known.

Table 1

Operating conditions that do not cause soot formation (taken from the paper by Christensen and Primdahl, 1994).

It is advantageous to operate the method at a low steam to carbon ratio because the low ratio reduces the investment cost of the ATR device and reduces the energy consumption necessary to operate the device. In addition, the low steam-to-carbon ratio makes it possible to optimize the synthesis gas composition produced, which is used for the production of CO-rich gas such as methanol or dimethyl ether synthesis and Fischer-Tropsch process.

It has been found that arranging a low temperature reforming reactor with a steam reforming catalyst upstream of the autothermal reformer reduces the critical ratio of steam to carbon. The steam reforming reactor removes or reduces the content of higher hydrocarbons. Higher hydrocarbons are hydrocarbons composed of two or more carbon atoms. The steam reforming catalyst converts higher hydrocarbons into a mixture of methane, carbon monoxide, carbon dioxide and hydrogen.

The low temperature steam reforming reactor may be an adiabatic prereformer or a heated prereformer, for example in the form of a catalyzed heat exchanger coil, as described in European Patent Publication No. 855,366. The outlet temperature of the effluent stream obtained from the low-temperature steam reforming reactor is not higher than 600°C.

Therefore, the present invention provides a method for preparing hydrogen-rich and/or carbon monoxide-rich gas through the catalytic autothermal conversion of hydrocarbon feedstock in an autothermal converter. The method further includes the steps of: (a) feeding hydrocarbon Pass through a first reactor containing a steam reforming catalyst to substantially remove higher hydrocarbons in the hydrocarbon feed; (b) pass the effluent from the first reactor to an autothermal reformer; and (c) change from autothermal The product gas rich in hydrogen and carbon monoxide is taken out from the vessel.

As an advantage of the present invention, it will be possible to operate the autothermal reactor at a lower steam to carbon ratio than when an unconverted feed stream is used as the autothermal reformer feed.

As a second advantage, when it does not contain higher hydrocarbons, the ATR feed gas can be preheated to a higher temperature. The result is a lower oxygen consumption of the method.

The present invention is particularly effective for steam conversion of associated gas. Associated gas is natural gas produced during oil production. Because it is not economical to transport associated gas, this gas is usually burned by a torch during drilling. Associated gas has a high content of higher hydrocarbons.

Example 1 The test device consists of a system for supplying feed to the ATR reactor, the ATR reactor and equipment for product gas post-treatment.

The feed stream consists of natural gas, steam, oxygen, hydrogen and optionally butane. The composition of natural gas is listed in Table 2. Compress all gases to operating pressure and preheat to operating temperature. The natural gas is desulfurized before being fed into the ATR reactor. The feed is mixed into two streams and sent to the combustion furnace of the ATR. The first feed stream contains natural gas, hydrogen, steam and optionally butane. This feed stream is heated to 500°C. The other feed stream contains oxygen and steam and is heated to 220°C. The pressure in the ATR reactor is 2.46 MPa. Preferably, the steam-containing natural gas passes through a pre-reformer before being fed into the ATR reactor. Also in this case, the gas stream is heated to 500°C before being fed into the ATR reactor.

Table 2

The composition of natural gas.

In the ATR reactor, sub-stoichiometric combustion and subsequent catalytic steam conversion and transfer reactions are carried out. Use gas chromatography to determine the composition of incoming and outgoing gases.

Downstream of the ATR reactor, the product gas is cooled and most of the vapor content of the product gas is condensed. If soot is formed, it is trapped in the condensate. The condensate is subjected to gravimetric analysis and spectrophotometric analysis and detection.

The following experiment was performed to demonstrate the effect of feed gas passing through the pre-reformer. In one experiment, the feed gas was mixed with butane. The butane concentration is 4.0% (volume) of the entire hydrocarbon.

Do each test with the critical ratio of steam to carbon approaching from the rich steam side. Start the test with a sufficiently high vapor flow to ensure soot-free conditions. Then gradually reduce the vapor flow. Let the system become stable. After stabilization, check the soot content in the condensate. If there is still no soot in the condensate, proceed to the next step. The term "soot-free conditions" refers to the conditions under which soot formation is negligible. The amount of soot formed at the critical ratio of steam to carbon is about 3-5 ppm.

In the test described below, the carbon flow rate is 100-103Nm3/h. The hydrogen flow rate is 2Nm3/h. The steam flow rate is adjusted to obtain a certain steam to carbon ratio. The oxygen flow rate is adjusted to obtain the desired operating temperature and is in the range of 55-58Nm3/h.

Due to the heat loss from the relatively small pilot plant, the adiabatic ATR outlet temperature will be higher than the temperature given in Table 3. Large-scale industrial installations will be very close to adiabatic conditions. Therefore, when the industrial installations are operated strictly under the same conditions as listed in Table 3, the outlet temperature of this device will be very close to the insulation values given in Table 3.

table 3

In the test of Table 3, the product gas composition obtained from the ATR reactor was determined by gas chromatography. The gas composition is shown in Table 4. The gas composition is given in dry mole percent. It is the molar composition of the gas component when it does not contain vapor.

Table 4

The test product gas composition (dry mole %) of Table 3 can be seen from Table 3 that the critical ratio of steam to carbon decreases when the feed steam passes through the pre-reformer. Moreover, it shows that increasing the butane content in the feed gas added to the ATR leads to an increase in the critical ratio of steam to carbon. This means that if the feed contains a large amount of higher hydrocarbons, the superiority of the feed through the pre-reformer will increase.

Example 2 uses the same test device as Example 1. In trials 2 and 3, ethane and butane were added to the feed stream containing natural gas.

In the test described below, the carbon flow rate was 102-103 Nm3/h. The hydrogen flow rate is 3Nm3/h. The steam flow rate is adjusted to obtain a certain steam to carbon ratio, and the oxygen flow rate is adjusted to obtain the desired operating temperature and is between 58-60Nm3/h.

table 5

The composition of the product gas obtained from the ATR reactor in the test in Table 5 is shown in Table 6.

Table 6

The test product gas composition of Table 5 (dry mole %) It can be seen from Table 5 that the high content of ethane and butane leads to an increase in the vapor to carbon ratio.