CN110630998B - Heat exchange process and heat exchange system of ethylene cracking furnace - Google Patents
Heat exchange process and heat exchange system of ethylene cracking furnace Download PDFInfo
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Abstract
The invention belongs to the field of petrochemical industry, and relates to a heat exchange process and a heat exchange system of an ethylene cracking furnace. In the heat exchange process, boiler feed water preheated by the convection section of the cracking furnace is divided into two paths, one path of the boiler feed water continuously enters the convection section for further preheating, then enters a steam drum for heat exchange with cracking gas in a first quenching heat exchanger group, and the other path of the boiler feed water enters a second quenching heat exchanger group for heat exchange with the cracking gas from the first quenching heat exchanger group, so that the temperature of the cracking gas is further reduced, and meanwhile, the boiler feed water is further heated, so that the heat of the cracking gas is further recovered. The energy-saving process of the invention obviously improves the energy utilization rate of the device, realizes energy conservation and consumption reduction in the production process, increases the yield of ultrahigh pressure steam and improves the economic benefit of the ethylene cracking device. In addition, the process technology is beneficial to the coking process of the furnace tube and the quenching heat exchanger in the device, and is beneficial to the safe, long-term and efficient operation of the production device.
Description
Technical Field
The invention belongs to the field of petrochemical industry, and particularly relates to an ethylene cracking furnace heat exchange process and an ethylene cracking furnace heat exchange system.
Background
The ethylene cracking furnace is a process device for generating ethylene and producing a byproduct of ultrahigh pressure steam by performing steam thermal cracking on petrochemical raw materials such as naphtha, diesel oil, hydrogenation tail oil, ethane, propane, LPG and the like, and is also the most energy-consuming part in the whole ethylene production device, and the energy consumption of the device accounts for 50-60% of the total energy consumption of ethylene production. Effectively improving the heat efficiency and the steam output of the cracking device, and is the key point for realizing energy conservation, consumption reduction and economic benefit improvement in the ethylene production process.
As shown in fig. 1, a general ethylene cracking furnace mainly comprises a cracking furnace body, a quenching heat exchanger and a high-pressure steam drum, wherein the cracking furnace body is divided into a convection section and a radiation section, and a plurality of heat exchange sections such as a raw material preheating section, a boiler water supply preheating section, a dilution steam superheating section, an upper mixing superheating section, an ultrahigh pressure steam superheating section and a lower mixing superheating section are sequentially distributed in the convection section. During normal cracking, the temperature of the cracking gas flowing out of the outlet of the radiation section of the cracking furnace is up to over 800 ℃, and in order to inhibit the secondary reaction of the cracking gas and improve the yield of olefin, the high-temperature cracking gas needs to be rapidly cooled in a quenching mode. At present, the quenching processes of the cracking gas mainly comprise three types, namely a first-stage quenching heat exchange process, a second-stage quenching heat exchange process and a third-stage quenching heat exchange process. For the first-stage quenching heat exchange process, high-temperature cracking gas at the outlet of a coil pipe at the radiation section of the cracking furnace enters a first-stage quenching heat exchanger, the cracking gas is cooled by high-pressure boiler feed water from a steam drum, the boiler feed water after heat exchange returns to the steam drum, and ultrahigh-pressure steam is a byproduct. For the traditional two-stage quenching heat exchange process, high-temperature cracking gas at the outlet of the radiation coil of the cracking furnace sequentially passes through the first-stage quenching heat exchanger and the second-stage quenching heat exchanger, high-pressure boiler feed water from a steam drum exchanges heat with the cracking gas and then returns to the steam drum, and ultrahigh-pressure steam is a byproduct. For the traditional primary quenching heat exchange process and the secondary quenching heat exchange process, because the heat exchange medium is saturated boiler feed water from a steam drum, the saturation temperature of the boiler feed water is about 324 ℃ according to the pressure grade of steam, the temperature of pyrolysis gas cannot be further reduced to be lower through heat exchange, and in order to meet the feeding requirement of a downstream separation device, the pyrolysis gas is often required to be further reduced by additionally arranging an oil quencher device. The above process can be adapted to the cracking of liquid and gas raw materials. The three-stage quenching heat exchange process is a process flow which adds a first-stage quenching heat exchanger on the basis of a second-stage quenching heat exchange process to reduce the temperature of the cracked gas to below 260 ℃ without adding an oil quencher device. This scheme can be used for cracking of gaseous feedstocks.
The inventor of the invention finds in research that in the existing three-stage quenching heat exchange technology, pyrolysis gas exchanges heat with raw material hydrocarbon in a third-stage quenching heat exchanger, the cooled pyrolysis gas is sent to a separation zone prefractionation device, and the preheated raw material hydrocarbon is used as a feed raw material of a cracking furnace. The process improves the utilization rate of heat to a certain extent, so that the steam yield is increased, but in practical application, because the temperature of the raw material hydrocarbon is lower, the pyrolysis gas is easy to condense and coke when entering the third-stage quenching heat exchanger, the heat exchange efficiency of the heat exchanger is seriously influenced, and the heat is not fully utilized by the third-stage quenching heat exchange process. And along with the continuous occurrence of condensation coking, the cracking gas outlet pipeline is further blocked, so that the heat exchange efficiency is further reduced, the pressure drop of the pipeline is greatly improved, the normal production is influenced, and the operation period of the device is shortened.
Therefore, how to optimize the quenching heat exchange flow of the cracking gas not only improves the heat utilization rate of the device, but also reduces the occurrence of coking reaction, so that the production device can run safely, long-term and efficiently, and the method is an important subject worth deep exploration of the ethylene cracking process.
Disclosure of Invention
The invention aims to: the invention solves the problems of high energy consumption and insufficient energy utilization in the existing cracking furnace heat exchange technology, and provides a heat exchange process and a heat exchange system of an ethylene cracking furnace.
In order to achieve the above object, a first aspect of the present invention provides an ethylene cracking furnace heat exchange process for cracking a gas feedstock: boiler feed water preheated by the convection section of the cracking furnace is divided into two paths, one path of the boiler feed water continuously enters the convection section for further preheating, then enters a steam drum for heat exchange with cracking gas in a first quenching heat exchanger group, and the other path of the boiler feed water enters a second quenching heat exchanger group for heat exchange with the cracking gas from the first quenching heat exchanger group, so that the temperature of the cracking gas is further reduced, and meanwhile, the boiler feed water is further heated, so that the heat of the cracking gas is further recovered.
According to the invention, the first quench exchanger bank may comprise one or two stages of quench exchangers, each stage of quench exchangers may comprise one or more. The second quenching heat exchanger group may be a second stage quenching heat exchanger or a third stage quenching heat exchanger according to the difference of the stage number of the first quenching heat exchanger group, and may also comprise one or more than one quenching heat exchanger.
According to a preferred embodiment of the present invention, as shown in fig. 5, the first quenching heat exchanger set comprises two stages of quenching heat exchangers connected in series, namely a first stage quenching heat exchanger and a second stage quenching heat exchanger; the second quench heat exchanger bank comprises a third stage quench heat exchanger;
after coming out from a radiant section furnace tube of the cracking furnace, the cracking gas sequentially passes through a first-stage quenching heat exchanger, a second-stage quenching heat exchanger and a third-stage quenching heat exchanger; the pyrolysis gas exchanges heat with boiler feed water from a steam drum through thermosyphon in a first-stage quenching heat exchanger and a second-stage quenching heat exchanger to generate steam, and exchanges heat with the other path of boiler feed water preheated by a convection section in a third-stage quenching heat exchanger. The process is referred to as the energy saving process 1. The energy-saving flow 1 is a preferred embodiment of the present invention.
According to another preferred embodiment of the present invention, as shown in FIG. 6, the first quench exchanger bank comprises only first stage quench exchangers; the second quench heat exchanger bank comprises a second stage quench heat exchanger;
after coming out from a radiant section furnace tube of the cracking furnace, the cracking gas sequentially passes through a first-stage quenching heat exchanger and a second-stage quenching heat exchanger; the pyrolysis gas exchanges heat with boiler feed water from a steam drum through thermosiphon in a first-stage quenching heat exchanger to generate steam, and exchanges heat with the other path of boiler feed water preheated by a convection section in a second-stage quenching heat exchanger. The flow is simply referred to as energy-saving flow 2.
In the two technical processes, the first stage quenching heat exchanger is in the form of a linear quenching heat exchanger or a traditional quenching heat exchanger, and the second stage quenching heat exchanger and the third stage quenching heat exchanger are in the form of horizontal shell-and-tube quenching heat exchangers.
For the first stage quench exchanger, when a conventional quench exchanger is employed, it may be of the conventional double tube-in-tube or thin tube sheet shell and tube type.
According to the present invention, the cracking feedstock of the cracking furnace may be various gaseous feedstocks such as ethane, propane, LPG, etc.
According to the invention, the boiler feed water preheating section of the ethylene cracking furnace is divided into an upper boiler feed water preheating section and a lower boiler feed water preheating section; after all the boiler feed water is preheated by the upper boiler feed water preheating section, part of the boiler feed water is sent to a second quenching heat exchanger group to exchange heat with pyrolysis gas; and the other part of boiler feed water enters a lower boiler feed water preheating section for continuous preheating and then enters a steam drum. In particular, the amount of the solvent to be used,
for the energy-saving process 1, as shown in fig. 5, after all the boiler feed water is preheated by the upper boiler feed water preheating section, a part of the boiler feed water is sent to the third-stage quenching heat exchanger to exchange heat with the pyrolysis gas; the other part of boiler feed water enters a lower boiler feed water preheating section for continuous preheating and then is sent to a high-pressure steam drum; boiler feed water coming out of the third-stage quenching heat exchanger is directly sent to a high-pressure steam drum to be used for generating ultrahigh-pressure steam.
For the energy-saving process 2, as shown in fig. 6, after all the boiler feed water is preheated by the upper boiler feed water preheating section, a part of the boiler feed water is sent to the second-stage quenching heat exchanger to exchange heat with the pyrolysis gas; the other part of boiler feed water enters a lower boiler feed water preheating section for continuous preheating and then is sent to a high-pressure steam drum; boiler feed water coming out of the second-stage quenching heat exchanger is directly sent to a high-pressure steam drum to be used for generating ultrahigh-pressure steam.
According to the invention, the temperature of the pyrolysis gas is reduced to 170-260 ℃ after the pyrolysis gas is subjected to heat exchange by the second quenching heat exchanger group. In particular, the amount of the solvent to be used,
in the energy-saving process 1, after the pyrolysis gas is discharged from the third-stage quenching heat exchanger, the temperature is reduced to 170-260 ℃, and the pyrolysis gas can be directly sent to a downstream separation device without setting quenching oil for a quenching device to continuously reduce the temperature.
In the energy-saving process 2, the temperature of the cracked gas is reduced to below 260 ℃, preferably 170-260 ℃, after the cracked gas is discharged from the second-stage quenching heat exchanger, the cracked gas can be directly sent to a downstream separation device, and the quenching oil for a quenching device is not required to be arranged for continuously reducing the temperature.
The specific cooling temperature needs to be determined according to the composition of the gas raw material, and particularly for the ethane raw material, as the heavy components of the cracking product are almost not available, the temperature of the cracking gas is reduced to 170-180 ℃ after the heat exchange of the second quenching heat exchanger group. Other gaseous materials need to be determined on a case-by-case basis.
According to the invention, the boiler feed water coming out of the upper boiler feed water preheating section is divided into two paths, and flow distribution is realized through a regulating valve, wherein the regulating valve is arranged on a boiler feed water pipeline going to the second quenching heat exchanger group or on a boiler feed water pipeline entering the lower boiler feed water preheating section; preferably, the boiler feed water flow entering the second quenching heat exchanger group or the boiler feed water flow entering the lower boiler feed water preheating section is controlled by a temperature regulating valve, and the distribution of the boiler feed water flow is realized by controlling the outlet temperature of the boiler feed water. The boiler feed water amount to the second quenching heat exchanger group accounts for 0-70% of the total boiler feed water amount, and the corresponding boiler feed water amount to the lower boiler feed water preheating section accounts for 30-100% of the total boiler feed water amount. When the cracking furnace tube or the quenching heat exchanger is burnt, the boiler feed water flow entering the second quenching heat exchanger group is reduced until the boiler feed water flow is zero, and the boiler feed water flow entering the lower boiler feed water preheating section is increased.
In particular, the amount of the solvent to be used,
in the energy-saving process 1, preferably, a temperature regulating valve is disposed on a boiler feed water feed pipe of the third-stage quench heat exchanger, and the distribution of the boiler feed water flow is realized by controlling the outlet temperature of the boiler feed water of the third-stage quench heat exchanger. When the furnace tube of the cracking furnace is burnt, the boiler feed water amount entering the third-stage quenching heat exchanger is reduced to zero at least according to the requirement, and most or all boiler feed water enters the lower boiler feed water preheating section for sufficient heat exchange, so that the exhaust gas temperature of the cracking furnace is reduced, and the heat efficiency is improved. When the quenching heat exchanger is used for burning, the boiler water supply quantity entering the lower boiler water supply preheating section is increased through the regulating valve, the boiler water supply quantity entering the third-stage quenching heat exchanger is reduced, and the boiler water supply quantity can be reduced to zero at least as required, so that the third-stage quenching heat exchanger has higher wall temperature, and the coke cleaning effect is improved.
In the energy-saving process 2, preferably, a temperature regulating valve is disposed on the boiler feed water feed pipe of the second stage quench heat exchanger, and the distribution of the boiler feed water flow is realized by controlling the outlet temperature of the boiler feed water of the second stage quench heat exchanger. When the furnace tube of the cracking furnace is burnt, the boiler water supply amount entering the second-stage quenching heat exchanger is reduced to zero at least according to the requirement, and most or all boiler water supply enters the lower boiler water supply preheating section for sufficient heat exchange, so that the smoke exhaust temperature of the cracking furnace is reduced, and the heat efficiency is improved. When the quenching heat exchanger is used for burning, the boiler water supply quantity entering the lower boiler water supply preheating section is increased through the regulating valve, the boiler water supply quantity entering the second-stage quenching heat exchanger is reduced, and the boiler water supply quantity can be reduced to zero at least as required, so that the second-stage quenching heat exchanger has higher wall temperature, and the coke cleaning effect is improved.
The second aspect of the invention provides an ethylene cracking furnace heat exchange system, which comprises a steam drum, a first quenching heat exchanger set and a second quenching heat exchanger set; the boiler water supply preheating section of the ethylene cracking furnace is divided into an upper boiler water supply preheating section and a lower boiler water supply preheating section communicated with the upper boiler water supply preheating section; the shell side of the first quenching heat exchanger group is communicated with a steam pocket through an ascending pipe and a descending pipe, and the pipe side is respectively communicated with an outlet of a furnace pipe of a radiant section of the cracking furnace and the second quenching heat exchanger group; and the shell pass of the second quenching heat exchanger group is respectively communicated with the outlet of the upper boiler water supply preheating section and the steam drum, and the tube pass is communicated with the first quenching heat exchanger group.
According to the invention, the first quench exchanger bank may comprise one or more quench exchangers, and the second quench exchanger bank may also comprise one or more quench exchangers.
According to a preferred embodiment of the present invention, the first quench exchanger bank comprises one or two quench exchangers; the second quench exchanger bank includes a primary quench exchanger.
According to a preferred embodiment of the present invention, the first stage quench heat exchanger of the first quench heat exchanger group is a vertical linear quench heat exchanger or a conventional quench heat exchanger; the other quenching heat exchangers (including the second quenching heat exchanger of the second quenching heat exchanger group) are horizontal shell-and-tube quenching heat exchangers. Specifically, in the above preferred embodiment, the first-stage quench heat exchanger is a vertical linear quench heat exchanger; the second stage quenching heat exchanger and the third stage quenching heat exchanger are horizontal shell-and-tube type quenching heat exchangers.
Wherein, the linear quenching heat exchanger is a double-pipe quenching heat exchanger, and can also be a U-shaped or inverted U-shaped quenching heat exchanger; the traditional quenching heat exchanger can be a double-sleeve type quenching heat exchanger or a thin-tube plate type quenching heat exchanger.
In order to realize flexible distribution of boiler feed water flow, preferably, a temperature regulating valve is arranged on a pipeline communicated with the outlet of the upper boiler feed water preheating section of the second quenching heat exchanger group.
The technical scheme of the invention has the following beneficial effects:
(1) the boiler feed water in the energy-saving process is divided into two paths, and the flow can be distributed according to different operation conditions, so that the device is more flexible to operate.
(2) Compare in traditional flow, the cooling of pyrolysis gas is all accomplished by the rapid cooling heat exchanger in the energy-conserving flow, need not to set up oil quencher device, consequently the heat of pyrolysis gas is absorbed by boiler feed water as much as possible for produce superhigh pressure steam, thereby greatly increased superhigh pressure steam output, greatly reduced ethylene cracker's energy consumption.
(3) The boiler feed water preheated by the convection section is used for exchanging heat with the cracked gas, and the temperature of the boiler feed water is higher, so that the wall temperature of a heat exchange tube exchanging heat with the cracked gas can be increased, and the condensation of heavy components of the cracked gas is effectively reduced, thereby slowing down coking, increasing the steam yield and further reducing the energy consumption.
(4) When the furnace tube of the cracking furnace is burnt, the energy-saving flow reduces the boiler water supply amount entering the second quenching heat exchanger group, so that the boiler water entering the lower boiler water supply preheating section can fully exchange heat, thereby reducing the smoke discharge temperature and improving the thermal efficiency of the cracking furnace.
(5) When the quenching heat exchanger is used for burning, the boiler water supply quantity entering the lower boiler water supply preheating section is increased through the regulating valve in the energy-saving process, so that the quenching heat exchanger exchanging heat with the other boiler water supply has higher wall temperature, and the burning effect of the quenching heat exchanger can be effectively improved.
(6) Compared with the prior art, the energy-saving process does not use hydrocarbon with lower temperature as a heat exchange medium, effectively reduces the occurrence of condensation coking in the quenching heat exchanger, not only improves the heat exchange efficiency of the device, but also is beneficial to prolonging the production period of the device and the safe, long-term and efficient operation of the production device.
Additional features and advantages of the invention will be set forth in the detailed description which follows.
Drawings
The above and other objects, features and advantages of the present invention will become more apparent by describing in more detail exemplary embodiments thereof with reference to the attached drawings, in which like reference numerals generally represent like parts throughout.
FIG. 1 is a schematic diagram of an ethylene cracking unit.
FIG. 2 is a schematic diagram of a primary quench heat exchange process of the prior art.
FIG. 3 is a schematic diagram of a two-stage quench heat exchange process of the prior art.
FIG. 4 is a schematic diagram of a three-stage quench heat exchange process of the prior art.
FIG. 5 is a schematic diagram of a three-stage quenching heat exchange energy-saving process of the present invention.
FIG. 6 is a schematic diagram of the two-stage quenching heat exchange energy-saving process of the present invention.
Description of reference numerals:
1. a radiation section of the cracking furnace; 2. a convection section of the cracking furnace; a. a raw material preheating section; b. boiler feed water preheating section: (BFW-I: upper boiler feed water preheating section, BFW-II: lower boiler feed water preheating section); c. a lower raw material preheating section; d. an upper mixing section and a lower ultrahigh-pressure steam preheating section; e. a medium and ultrahigh pressure steam preheating section; f. a lower ultrahigh pressure steam preheating section; g. a dilution steam superheating section; h. a lower mixing section; 3. a quench heat exchanger bank; 4. and (4) a steam drum.
Detailed Description
Preferred embodiments of the present invention will be described in more detail below. While the following describes preferred embodiments of the present invention, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein.
Example 1
In this example 1 (energy saving scheme 1), an ethylene plant cracking furnace as shown in FIG. 5 was used. The heat exchange system comprises a steam drum 4, a first quenching heat exchanger group and a second quenching heat exchanger group; the first quenching heat exchanger group comprises two stages of quenching heat exchangers in series connection, namely a first stage quenching heat exchanger and a second stage quenching heat exchanger; the second quenching heat exchanger group comprises a first-stage quenching heat exchanger which is a third-stage quenching heat exchanger; the first stage quenching heat exchanger is a vertical linear quenching heat exchanger; the second stage quenching heat exchanger and the third stage quenching heat exchanger are horizontal shell-and-tube type quenching heat exchangers. The boiler feed water preheating section b of the ethylene cracking furnace is divided into an upper boiler feed water preheating section BFW-I and a lower boiler feed water preheating section BFW-II communicated with the upper boiler feed water preheating section BFW-I; the shell passes of the first-stage quenching heat exchanger and the second-stage quenching heat exchanger are both communicated with the steam drum, and the tube passes are respectively communicated with the outlet of a furnace tube of the radiant section of the cracking furnace and the third-stage quenching heat exchanger; and the shell pass of the third-stage quenching heat exchanger is respectively communicated with the BFW-I outlet of the upper boiler water supply preheating section and the steam drum 4, and the tube pass is communicated with the second-stage quenching heat exchanger. And a pipeline communicated with the outlet of the upper boiler feed water preheating section BFW-I is provided with a temperature regulating valve.
After coming out from a radiant section furnace tube of the cracking furnace, the cracking gas sequentially passes through a first-stage quenching heat exchanger, a second-stage quenching heat exchanger and a third-stage quenching heat exchanger; the pyrolysis gas exchanges heat with boiler feed water from a steam drum through thermosiphon in a first-stage quenching heat exchanger and a second-stage quenching heat exchanger, and exchanges heat with the boiler feed water preheated by a convection section in a third-stage quenching heat exchanger.
All boiler feed water is preheated by an upper boiler feed water preheating section BFW-I, and then a part of boiler feed water is sent to a third-stage quenching heat exchanger to exchange heat with pyrolysis gas; and the other part of boiler feed water enters a lower boiler feed water preheating section BFW-II to be continuously preheated.
Comparative example 1
An ethylene plant cracking furnace as shown in figure 3 was used.
After coming out from a radiant section furnace tube of the cracking furnace, the pyrolysis gas sequentially passes through a first-stage quenching heat exchanger, a second-stage quenching heat exchanger and an oil quencher; wherein, pyrolysis gas exchanges heat with drum boiler feed water in the first and second-stage quenching heat exchangers, and the temperature is reduced by directly mixing quenching oil in an oil quencher.
In the flow, all the boiler feed water enters the steam drum 4 after being preheated by the boiler feed water preheating section b.
Comparative example 2
An ethylene plant cracking furnace as shown in figure 4 was used.
After coming out from a radiant section furnace tube of the cracking furnace, the cracking gas sequentially passes through a first-stage quenching heat exchanger, a second-stage quenching heat exchanger and a third-stage quenching heat exchanger; wherein, the pyrolysis gas exchanges heat with the boiler feed water of the steam drum in the first and second quenching heat exchangers, and exchanges heat with the raw material hydrocarbon in the third quenching heat exchanger.
In the flow, all the boiler feed water enters the steam drum 4 after being preheated by the boiler feed water preheating section b.
Example 2
In this example 2 (energy saving scheme 2), an ethylene plant cracking furnace as shown in FIG. 6 was used. The difference from the embodiment 1 is that: the flow only contains two stages of quenching heat exchangers.
After coming out from a radiant section furnace tube of the cracking furnace, the cracking gas sequentially passes through a first-stage quenching heat exchanger and a second-stage quenching heat exchanger; the pyrolysis gas exchanges heat with boiler feed water from a steam drum in a first quenching heat exchanger, and exchanges heat with the boiler feed water preheated by a convection section in a second quenching heat exchanger.
All boiler feed water is preheated by an upper boiler feed water preheating section BFW-I, and then a part of boiler feed water is sent to a second-stage quenching heat exchanger to exchange heat with pyrolysis gas; the other part of boiler feed water enters a lower boiler feed water preheating section BFW-II to be continuously preheated and then enters a steam drum 4.
Table 1 below shows a comparison of the process parameters for each run under the same feed conditions:
TABLE 1
| Comparative example 1 | Comparative example 2 | |
|
|
| Phase of operation | Initial stage | Initial stage | Initial stage | Initial stage |
| Number of stages of quench heat exchanger | Three-stage | Three-stage | Three-stage | Second stage |
| Hydrocarbon feed volume ton/hr | 44.50 | 44.50 | 44.50 | 44.50 |
| Dilution ratio | 0.3 | 0.3 | 0.3 | 0.3 |
| Ultrahigh pressure steam yield ton/hr | 55.55 | 58.6 | 63.76 | 63.76 |
| Hours of annual operation | 8000 | 8000 | 8000 | 8000 |
| Exhaust gas temperature C | 104 | 108 | 104 | 104 |
| Thermal efficiency% | 94.5 | 94.3 | 94.5 | 94.5 |
| Specific ethylene energy consumption kJ/kg (C2H4) | 8948 | 7561 | 7437 | 7437 |
The energy-saving process 1 with the three-stage quenching heat exchanger and the energy-saving process 2 with the two-stage quenching heat exchanger have the same thermal efficiency and the same technological parameters at the initial stage.
Compared with the comparative example 1, the steam yield of the energy-saving flow path is increased from 55.55 tons/h to 63.76 tons/h through the flow path improvement, which shows that the energy utilization rate of the ethylene cracking furnace is improved. Meanwhile, the unit ethylene energy consumption is reduced from 8948kJ/kg to 7437kJ/kg, which shows that the energy-saving process has better energy-saving benefit.
Compared with the comparative example 2, the steam yield of the energy-saving flow path is increased from 58.6 tons/h to 63.76 tons/h through flow path improvement, the thermal efficiency is improved from 94.3 percent to 94.5 percent, and the energy utilization rate of the ethylene cracking furnace is improved. Meanwhile, the unit ethylene energy consumption is reduced from 7561kJ/kg to 7437kJ/kg, which shows that the energy-saving process has better energy-saving benefit.
Having described embodiments of the present invention, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.
Claims (10)
1. The heat exchange process of the ethylene cracking furnace for cracking the gas raw material is characterized in that: boiler feed water preheated by the convection section of the cracking furnace is divided into two paths, one path of the boiler feed water continuously enters the convection section for further preheating, then enters a steam drum for heat exchange with cracking gas in a first quenching heat exchanger group, and the other path of the boiler feed water enters a second quenching heat exchanger group for heat exchange with the cracking gas from the first quenching heat exchanger group, so that the temperature of the cracking gas is further reduced, and meanwhile, the boiler feed water is further heated, so that the heat of the cracking gas is further recovered; the boiler water supply preheating section of the ethylene cracking furnace is divided into an upper boiler water supply preheating section and a lower boiler water supply preheating section; after all the boiler feed water is preheated by the upper boiler feed water preheating section, part of the boiler feed water is sent to a second quenching heat exchanger group to exchange heat with pyrolysis gas; and the other part of boiler feed water enters a lower boiler feed water preheating section for continuous preheating and then enters a steam drum.
2. The heat exchange process of the ethylene cracking furnace of claim 1, which is characterized in that: the first quenching heat exchanger group comprises two stages of quenching heat exchangers in series connection, namely a first stage quenching heat exchanger and a second stage quenching heat exchanger; the second quench heat exchanger bank comprises a third stage quench heat exchanger;
after coming out from a radiant section furnace tube of the cracking furnace, the cracking gas sequentially passes through a first-stage quenching heat exchanger, a second-stage quenching heat exchanger and a third-stage quenching heat exchanger; the pyrolysis gas exchanges heat with boiler feed water from a steam drum through thermosyphon in a first-stage quenching heat exchanger and a second-stage quenching heat exchanger to generate steam, and exchanges heat with the other path of boiler feed water preheated by a convection section in a third-stage quenching heat exchanger.
3. The heat exchange process of the ethylene cracking furnace of claim 1, which is characterized in that: the first quench heat exchanger bank comprises a first stage quench heat exchanger; the second quench heat exchanger bank comprises a second stage quench heat exchanger;
after coming out from a radiant section furnace tube of the cracking furnace, the cracking gas sequentially passes through a first-stage quenching heat exchanger and a second-stage quenching heat exchanger; the pyrolysis gas exchanges heat with boiler feed water from a steam drum through thermosiphon in a first-stage quenching heat exchanger to generate steam, and exchanges heat with the other path of boiler feed water preheated by a convection section in a second-stage quenching heat exchanger.
4. The heat exchange process of the ethylene cracking furnace of any one of claims 1 to 3, which is characterized in that: after the pyrolysis gas is subjected to heat exchange by the second quenching heat exchanger set, the temperature is reduced to 170-260 ℃.
5. The heat exchange process of the ethylene cracking furnace of any one of claims 1 to 3, which is characterized in that: the boiler feed water coming out of the upper boiler feed water preheating section is divided into two paths, and flow distribution is realized through a regulating valve, wherein the regulating valve is arranged on a boiler feed water pipeline going to the second quenching heat exchanger group or a boiler feed water pipeline entering the lower boiler feed water preheating section; the boiler feed water flow entering the second quenching heat exchanger group or the boiler feed water flow entering the lower boiler feed water preheating section is controlled by a temperature regulating valve, and the distribution of the boiler feed water flow is realized by controlling the outlet temperature of the boiler feed water.
6. The heat exchange process of the ethylene cracking furnace of claim 5, which is characterized in that: the boiler feed water amount to the second quenching heat exchanger group accounts for 0-70% of the total boiler feed water amount.
7. The heat exchange process of the ethylene cracking furnace of claim 5, which is characterized in that: when the cracking furnace tube or the quenching heat exchanger is burnt, the boiler water supply amount entering the second quenching heat exchanger group is reduced, and the boiler water supply amount entering the lower boiler water supply preheating section is increased.
8. The heat exchange system of the ethylene cracking furnace is characterized in that: the heat exchange system comprises a steam drum, a first quenching heat exchanger group and a second quenching heat exchanger group; the boiler water supply preheating section of the ethylene cracking furnace is divided into an upper boiler water supply preheating section and a lower boiler water supply preheating section communicated with the upper boiler water supply preheating section; the shell side of the first quenching heat exchanger group is communicated with a steam pocket through an ascending pipe and a descending pipe, and the pipe side is respectively communicated with an outlet of a furnace pipe of a radiant section of the cracking furnace and the second quenching heat exchanger group; and the shell pass of the second quenching heat exchanger group is respectively communicated with the outlet of the upper boiler water supply preheating section and the steam drum, and the tube pass is communicated with the first quenching heat exchanger group.
9. The heat exchange system of the ethylene cracking furnace of claim 8, wherein: the first quench heat exchanger bank comprises one-stage or two-stage quench heat exchangers; the second quench exchanger bank includes a primary quench exchanger.
10. The heat exchange system of the ethylene cracking furnace of claim 8, wherein: the first stage quenching heat exchanger of the first quenching heat exchanger group is a vertical linear quenching heat exchanger or a traditional quenching heat exchanger; the other quench heat exchangers are horizontal shell-and-tube quench heat exchangers.
Priority Applications (1)
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