Equipment and method for recovering propane, propylene and ethylene from chemical tail gas

Abstract

The equipment and method for recovering propane, propylene and ethylene from chemical tail gas of the present invention, wherein the equipment of the present invention comprises: a main heat exchanger; a distillation tower, connected to the main heat exchanger through a pipeline; a product separator, connected to the bottom outlet of the distillation tower through a pipeline; a tower top condenser, connected to the distillation tower through a pipeline; a cooling tower top separator, the non-condensable gas outlet of the cooling tower top separator is connected to the first pipeline, and the cooling tower top separator is connected to the distillation tower through a pipeline. The method for recovering propane, propylene and ethylene from chemical tail gas comprises: cooling the chemical tail gas; distilling the cooled chemical tail gas; separating the liquid phase; cooling the gas phase; and separating the cooled gas phase. The technical solution of the present invention has low energy consumption, is energy-saving and environmentally friendly, can turn waste into treasure, and greatly improves the added value of the product.

Description

Technical Field

[0001] The invention relates to the field of chemical industry, and in particular to a device and a method for recovering propane, propylene and ethylene from chemical tail gas. Background Art

[0002] Ethylene, propylene and propane are important chemical raw materials.

[0003] Ethylene, propylene, and propane products are valuable resources in refining and chemical companies and are the most basic chemical raw materials. In the production process of methanol to olefins, a portion of ethylene, propylene, propane and other products are taken away with the methane tail gas in the olefin separation unit and used as flare gas or fuel gas, resulting in a waste of resources. However, if the ethylene, propylene, propane and other products in the methane tail gas are taken out and used separately, the added value of the products will be greatly improved. Among them, the value of fuel gas is about 1,000 yuan / ton, while the value of ethylene, propylene, and propane as products is about 3,500 yuan / ton. Directly burning the ethylene, propylene, and propane products in the fuel gas causes huge waste. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a device and method for recovering propane, propylene and ethylene from chemical tail gas, which can fully extract components from tail gas of a methane tower and prepare mixed hydrocarbon products.

[0005] The equipment for recovering propane, propylene and ethylene from chemical tail gas of the present invention comprises:

[0006] Main heat exchanger for cooling chemical tail gas;

[0007] A distillation tower used to distill the chemical tail gas after cooling to obtain gas phase and liquid phase, which is connected to the main heat exchanger through a pipeline;

[0008] A product separator for separating the liquid phase to obtain C2+ products and fuel gas, connected to the bottom outlet of the distillation tower through a pipeline;

[0009] A tower top condenser for cooling the gas phase, connected to the distillation tower through a pipeline;

[0010] A cooling tower top separator for separating and treating the cooled gas phase to obtain non-condensable gas, wherein the non-condensable gas outlet of the cooling tower top separator is connected to the first pipeline, and the cooling tower top separator is connected to the distillation tower through the pipeline;

[0011] The first pipeline passes through the top condenser and the main heat exchanger in sequence and is connected to the inlet of the first-stage expansion machine, so that the non-condensable gas in the first pipeline is expanded, cooled and depressurized by the first-stage expansion machine after being restored to temperature in the top condenser and the main heat exchanger, the outlet of the first-stage expansion machine is connected to the second pipeline, the second pipeline passes through the main heat exchanger and is connected to the inlet of the second-stage expansion machine, so that the non-condensable gas in the second pipeline is expanded, cooled and depressurized by the second-stage expansion machine after being cooled by the main heat exchanger, the outlet of the second-stage expansion machine is connected to the third pipeline, the third pipeline passes through the top condenser and the main heat exchanger in sequence, so that the non-condensable gas in the third pipeline provides cooling capacity for the top condenser and the main heat exchanger.

[0012] The equipment for recovering propane, propylene and ethylene from chemical tail gas of the present invention comprises the following steps: the product separator is connected to the bottom outlet of the distillation tower through a fourth pipeline, and a low-temperature hydrocarbon mixing pump is arranged on the fourth pipeline.

[0013] The equipment for recovering propane, propylene and ethylene from chemical tail gas of the present invention, wherein the fourth pipeline is connected to the product separator after passing through the main heat exchanger, so that the liquid phase in the fourth pipeline provides cooling capacity for the main heat exchanger.

[0014] The method for recovering propane, propylene and ethylene from chemical tail gas of the present invention comprises:

[0015] Cooling of chemical exhaust gas;

[0016] The cooled chemical tail gas is distilled to obtain a gas phase and a liquid phase;

[0017] Separating the liquid phase to obtain C2+ products and fuel gas;

[0018] Cooling of the gas phase;

[0019] Used to separate the cooled gas phase to obtain non-condensable gas.

[0020] The method for recovering propane, propylene and ethylene from chemical tail gas of the present invention further comprises:

[0021] Treat the expansion and cooling and pressure reduction of non-condensable gas after reheating;

[0022] The non-condensable gas is cooled again, expanded, cooled and depressurized to provide cooling capacity for the main heat exchanger.

[0023] The technical solution of the present invention has a stable and reliable process, low energy consumption, energy saving and environmental protection, can turn waste into treasure, and greatly improve the added value of products. The technical solution of the present invention can fully extract the components in the tail gas of the methane tower to prepare mixed hydrocarbon products, improve economic benefits, and also improve the utilization efficiency of the methane tail gas, so that its added value is greatly increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1The present invention is a schematic diagram of the structure of the equipment for recovering propane, propylene and ethylene from chemical tail gas. DETAILED DESCRIPTION

[0025] like Figure 1 As shown, the equipment for recovering propane, propylene and ethylene from chemical tail gas of the present invention comprises:

[0026] Main heat exchanger E102 for cooling chemical tail gas;

[0027] A distillation tower T101 is used to distill the chemical tail gas after cooling to obtain gas phase and liquid phase, and is connected to the main heat exchanger through a pipeline;

[0028] A product separator V101 for separating the liquid phase to obtain C2+ products and fuel gas, connected to the bottom outlet of the distillation tower through a pipeline;

[0029] The top condenser E103 for cooling the gas phase is connected to the distillation tower through a pipeline;

[0030] A cooling tower top separator V102 for separating and treating the cooled gas phase to obtain non-condensable gas, wherein the non-condensable gas outlet of the cooling tower top separator is connected to the first pipeline 10, and the cooling tower top separator is connected to the distillation tower through a pipeline;

[0031] The first pipeline 10 passes through the top condenser and the main heat exchanger in sequence and is connected to the inlet of the first-stage expansion machine C101, so that the non-condensable gas in the first pipeline is expanded, cooled and depressurized by the first-stage expansion machine after being restored to temperature in the top condenser and the main heat exchanger. The outlet of the first-stage expansion machine is connected to the second pipeline 20, and the second pipeline is connected to the inlet of the second-stage expansion machine C102 after passing through the main heat exchanger, so that the non-condensable gas in the second pipeline is expanded, cooled and depressurized by the second-stage expansion machine after being cooled and depressurized by the main heat exchanger. The outlet of the second-stage expansion machine is connected to the third pipeline, and the third pipeline 30 passes through the top condenser and the main heat exchanger in sequence, so that the non-condensable gas in the third pipeline provides cooling for the top condenser and the main heat exchanger.

[0032] The equipment for recovering propane, propylene and ethylene from chemical tail gas of the present invention, wherein the product separator is connected to the bottom outlet of the distillation tower via a fourth pipeline, and a low-temperature hydrocarbon mixing pump P101 is provided on the fourth pipeline 40.

[0033] The equipment for recovering propane, propylene and ethylene from chemical tail gas of the present invention, wherein the fourth pipeline is connected to the product separator after passing through the main heat exchanger, so that the liquid phase in the fourth pipeline provides cooling capacity for the main heat exchanger.

[0034] The method for recovering propane, propylene and ethylene from chemical tail gas of the present invention comprises:

[0035] Cooling of chemical exhaust gas;

[0036] The chemical tail gas after cooling is subjected to distillation treatment to obtain a gas phase and a liquid phase;

[0037] Separating the liquid phase to obtain C2+ products and fuel gas;

[0038] Cooling of the gas phase;

[0039] Used to separate the cooled gas phase to obtain non-condensable gas.

[0040] The method for recovering propane, propylene and ethylene from chemical tail gas of the present invention further comprises:

[0041] Treat the expansion, cooling and pressure reduction of non-condensable gas after reheating;

[0042] The non-condensable gas is cooled again, expanded, cooled and depressurized to provide cooling capacity for the main heat exchanger.

[0043] The equipment and method for recovering propane, propylene and ethylene from chemical tail gas of the present invention relate to a process method for recovering effective components such as propane, propylene and ethylene from the tail gas at the top of a methanol to olefin demethanizer. The characteristics are: the demethanizer of the olefin separation unit of the MTO device adopts a low-temperature propane or propylene washing method to recover C2 and above components in the raw gas, and the tail gas dissolved by propane washing in the demethanizer contains a large amount of methane, hydrogen, nitrogen, carbon monoxide, ethylene, propane, propylene, C4 and other components. The tail gas at the top of the methane tower is first cooled to a certain temperature through a heat exchanger, and the cooled raw gas is separated through a low-temperature distillation tower, and a qualified C2+ product is produced from the bottom of the tower and sent out of the boundary area after being pressurized and reheated by a low-temperature mixed hydrocarbon pump. The non-condensable gas (fuel gas) produced from the top of the tower is first reheated to a certain temperature through a heat exchanger and enters a primary expander to expand to a certain pressure, and then enters a heat exchanger again to heat to a certain temperature and then enters a secondary expander to expand to a certain pressure and temperature to provide coldness in the lowest temperature zone at the top of the distillation tower. The tail gas after being reheated at the top of the distillation tower is reheated again in the main heat exchanger and sent to the fuel gas official website.

[0044] This process utilizes the tail gas from the top of the demethanizer tower to extract the C2+ product from the tail gas of the methane tower by means of expansion refrigeration and cryogenic distillation separation by an expander, and the remaining gas is sent to the fuel gas pipeline network as fuel gas.

[0045] The tail gas after propane washing and dissolution in the demethanizer contains a large amount of methane, hydrogen, nitrogen, carbon monoxide, ethylene, propane, propylene, C4, etc. The tail gas at the top of the methane tower is first cooled to a certain temperature through a heat exchanger. The cooled raw gas is separated by a low-temperature distillation tower, and qualified C2+ products are produced from the bottom of the tower and sent out of the boundary area after being pressurized and reheated by a low-temperature mixed hydrocarbon pump. The non-condensable gas (fuel gas) produced from the top of the tower is first reheated to a certain temperature through a heat exchanger, enters the first-stage expansion machine to expand to a certain pressure, enters the heat exchanger again to heat to a certain temperature, and then enters the second-stage expansion machine to expand to a certain pressure and temperature to provide cooling capacity for the top of the distillation tower. The tail gas after reheating at the top of the distillation tower is reheated again in the main heat exchanger and sent to the fuel gas official website.

[0046] The main heat exchanger can be plate-fin type, coiled tube type, or plate type.

[0047] The tail gas from the top of the methane tower is first cooled to a certain temperature through a heat exchanger, and the cooled raw gas is separated through a low-temperature distillation tower. The cooling temperature range is generally between -30℃ and -120℃.

[0048] Qualified C2+ products are produced from the bottom of the tower. C2+ generally contains ethylene, propylene, propane, isobutane, n-butane, etc.

[0049] The non-condensable gas (fuel gas) produced from the top of the tower is first reheated to a certain temperature through a heat exchanger, and the reheating range is generally between -130℃ and -50℃.

[0050] The non-condensable gas enters the first-stage expander and expands to a certain pressure. The pressure range after expansion is generally between 1.8MPa and 1.2MPa.

[0051] The expander is a turbine type, and generally oil bearing expander and gas bearing expander can be selected.

[0052] The non-condensable gas enters the heat exchanger again to exchange heat to a certain temperature, and then enters the secondary expander to expand to a certain pressure and temperature. The temperature range of entering the secondary expander is generally between -60℃ and -120℃. The pressure range after secondary expansion is generally between 1.6MPa and 0.1MPa.

[0053] The non-condensable gas provides cooling capacity for the lowest temperature zone at the top of the distillation tower. The temperature at the top of the distillation tower is generally between -120℃ and -145℃.

[0054] The recovery rate of C2+ mixed hydrocarbons can reach between 92% and 98%.

[0055] The C2+ product is pressurized and reheated by a low-temperature hydrocarbon mixing pump and then sent out of the boundary area. After reheating, it is directly sent to the olefin separation unit for separation.

[0056] The C2+ product passes through a cryogenic hydrocarbon mixing pump, which may be a shielded pump, a cryogenic submersible pump, a centrifugal pump, or a reciprocating pump.

[0057] The technical solution of the present invention has stable and reliable process and low energy consumption, and achieves the effects of energy saving and environmental protection, turning waste into treasure, and greatly improving the added value of products.

[0058] The tail gas from the demethanizer passes through the reboiler E101 and the main heat exchanger, is cooled to -30℃~-130℃, and enters the low-temperature distillation tower. The liquid product is extracted from the top of the tower, pressurized by the low-temperature mixing pump, and then reheated by the main heat exchanger before being sent out of the boundary area.

[0059] The gas phase at the top of the tower is condensed by the tower top condenser and then the liquid phase flows back to the tower. The gas phase is reheated to -120℃~-60℃ by the main heat exchanger and then enters the first-stage expander. The expanded tail gas is reheated by heat exchange and then enters the second-stage expander. The expanded tail gas is heat exchanged with the tail gas at the top of the cryogenic distillation tower and finally reheated by the main heat exchanger and then sent out of the boundary area. The cooling capacity of the entire system is provided by the expander.

[0060] The above are only preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A device for recovering propane, propylene and ethylene from chemical tail gas, characterized in that: include: Main heat exchanger for cooling chemical tail gas; A distillation tower used to distill the chemical tail gas after cooling to obtain gas phase and liquid phase, which is connected to the main heat exchanger through a pipeline; A product separator for separating the liquid phase to obtain C2+ products and fuel gas, connected to the bottom outlet of the distillation tower through a pipeline; A tower top condenser for cooling the gas phase, connected to the distillation tower through a pipeline; A cooling tower top separator for separating and treating the cooled gas phase to obtain non-condensable gas, wherein the non-condensable gas outlet of the cooling tower top separator is connected to the first pipeline, and the cooling tower top separator is connected to the distillation tower through the pipeline; The first pipeline passes through the top condenser and the main heat exchanger in sequence and is connected to the inlet of the first-stage expansion machine, so that the non-condensable gas in the first pipeline is expanded, cooled and depressurized by the first-stage expansion machine after being reheated in the top condenser and the main heat exchanger, the outlet of the first-stage expansion machine is connected to the second pipeline, the second pipeline passes through the main heat exchanger and is connected to the inlet of the second-stage expansion machine, so that the non-condensable gas in the second pipeline is expanded, cooled and depressurized by the second-stage expansion machine after being reheated in the main heat exchanger, the outlet of the second-stage expansion machine is connected to the third pipeline, the third pipeline passes through the top condenser and the main heat exchanger in sequence, so that the non-condensable gas in the third pipeline provides cooling for the top condenser and the main heat exchanger.

2. The equipment for recovering propane, propylene and ethylene from chemical tail gas as claimed in claim 1, characterized in that: The product separator is connected to the bottom outlet of the distillation tower through a fourth pipeline, and a low-temperature hydrocarbon mixing pump is arranged on the fourth pipeline.

3. The equipment for recovering propane, propylene and ethylene from chemical tail gas as claimed in claim 2, characterized in that: The fourth pipeline is connected to the product separator after passing through the main heat exchanger, so that the liquid phase in the fourth pipeline provides cooling capacity for the main heat exchanger.

4. A method for recovering propane, propylene and ethylene from chemical tail gas using the equipment described in any one of claims 1 to 3, characterized in that: include: Cooling of chemical exhaust gas; The cooled chemical tail gas is distilled to obtain a gas phase and a liquid phase; Separating the liquid phase to obtain C2+ products and fuel gas; Cooling of the gas phase; Used to separate the cooled gas phase to obtain non-condensable gas.

5. The method for recovering propane, propylene and ethylene from chemical tail gas as claimed in claim 4, characterized in that: Also includes: Treat the expansion and cooling and pressure reduction of non-condensable gas after reheating; The non-condensable gas is then heat exchanged, reheated, expanded, cooled, and depressurized to provide cooling for the main heat exchanger.

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