Method for evaluating carbon footprint of regenerator of catalytic cracking unit

Abstract

The invention provides a method for evaluating carbon footprint of a regenerator of a catalytic cracking device, and relates to the technical field of oil refining production. According to the method for evaluating the carbon footprint of the regenerator of the catalytic cracking device, input material flows of the regenerator comprise coke-burning main air, a spent catalyst and deoxygenated water, output material flows comprise flue gas, a regenerated catalyst and steam, and carbon emission in the coke-burning process is accompanied by release, utilization, recovery and discharge of energy. Carbon footprint evaluation on the regenerator should be carried out according to an energy output or utilization mode to distribute carbon emission and quantify the carbon emission into corresponding material flows, including a regenerant carbon footprint, a steam carbon footprint and a flue gas carbon footprint.

Description

Technical Field

[0001] This invention relates to a method for evaluating the carbon footprint of regenerators in catalytic cracking units in the field of oil refining. It is particularly applicable to catalyst regeneration processes that utilize flue gas turbines and waste heat boilers to recover flue gas energy. Applying this method to allocate carbon emissions can reflect the direct relationship between energy utilization and carbon emissions. Background Technology

[0002] Product carbon footprint assessment calculates greenhouse gas emissions generated by a product during its life cycle stages, including raw material acquisition, transportation, production, and use, based on the life cycle concept. It is typically expressed in carbon dioxide mass equivalent (CO2). 2e () is the unit of evaluation.

[0003] Catalytic cracking units are important secondary units in the oil refining process. Their main function is to produce light fractions such as gasoline and liquefied petroleum gas by cracking, condensation, and hydrogen transfer of heavy feedstocks such as vacuum gas oil, atmospheric residue, and vacuum residue under the action of a catalyst. The catalyst will be deactivated due to coking during the reaction process and generally needs to be regenerated by burning the coke.

[0004] Catalytic cracking units typically consist of reaction-regeneration, fractionation, absorption stabilization, rich gas compressor units, main blowers and flue gas energy recovery units, flue gas waste heat boilers, and flue gas desulfurization and denitrification systems.

[0005] The reaction-regeneration system is the core component of the unit, where both feedstock cracking and catalyst regeneration are completed. The system includes a riser reactor, reaction settling tank, regenerator, internal and external heat exchangers, catalyst tank, and special valves for the reaction-regeneration system. The main blower, responsible for supplying coke-burning air to the regenerator, is a crucial part of the unit. Reaction-regeneration systems can be configured in various ways; currently, most are equipped with an energy recovery system, including a main blower-flue gas turbine unit, booster compressor, and waste heat boiler, with the process as follows: Figure 1 As shown.

[0006] Figure 1 This is a schematic diagram of the absorption stabilization system of a catalytic cracking unit.

[0007] exist Figure 1In the process, air is compressed by the main fan and enters the regenerator. The deactivated catalyst (the catalyst awaiting regeneration) due to carbon buildup enters the regenerator through the settling tank of the reaction unit. The carbon buildup on the catalyst undergoes a coking reaction in the high-temperature environment of the regenerator, releasing a large amount of energy and generating carbon emissions. The high-temperature regenerated flue gas, after catalyst separation, enters the flue gas turbine, which drives the main fan. After exiting the turbine, the flue gas enters the waste heat boiler to recover the remaining energy. In the above process, the carbon emissions from the regenerator are mainly caused by the coking process. The energy released in this process is directly related to its carbon emissions. The energy generated by coking has three main uses: first, it heats the air used in the coking process and is carried out of the regenerator as it becomes flue gas; second, it transfers heat from the regenerator to the reactor through the circulation of the catalyst between the regenerator and the reactor, and through the catalyst's heat-carrying effect; that is, the material cycle between the reactor and the regenerator involves the regenerator supplying energy to the reactor; and third, the remaining heat from the regenerator is extracted through a heat exchanger to generate steam.

[0008] The flue gas exiting the regenerator has a high temperature and pressure. Part of its energy can be recovered and utilized through a flue gas turbine and waste heat boiler. Therefore, the flue gas exiting the regenerator is an intermediate product, requiring two downstream stages: a flue gas turbine and a waste heat boiler. Consequently, carbon emission allocation for the regenerator flue gas is necessary. Simultaneously, as an auxiliary power source for the main fan, the carbon emissions of the flue gas turbine should also be included in the main fan's emissions, thus establishing a connection with the flue gas emissions.

[0009] The carbon emissions and heat load of the regenerator in a catalytic cracking unit are relatively large, and conducting a carbon footprint assessment of the regenerator is crucial for constructing a carbon footprint system for the catalytic cracking unit. Summary of the Invention

[0010] This invention proposes a method for evaluating the carbon footprint of a regenerator in a catalytic cracking unit. The input streams of the regenerator include: coking air, recycled catalyst, and deoxygenated water, while the output streams include: flue gas, regenerated catalyst, and steam. Carbon emissions from the coking process are accompanied by the release, utilization, recovery, and disposal of energy. The carbon footprint evaluation of the regenerator should allocate carbon emissions according to the energy output or utilization method and quantify them into the corresponding streams, including the carbon footprint of the regenerator, the carbon footprint of steam, and the carbon footprint of flue gas.

[0011] (1) Carbon footprint of flue gas The high-temperature flue gas carries a large amount of energy as it exits the regenerator, and this energy is recovered and utilized downstream. The carbon emissions from the coking process should be allocated to the flue gas based on energy balance. The high-temperature flue gas then enters the flue gas turbine and waste heat boiler, where the recovered energy is... and This portion of energy should be allocated to corresponding carbon emissions.

[0012] Flue gas enters the flue gas turbine to recover heat energy. ) and convert it into power energy, which drives the main fan to provide the main air for burning coke, and the flue gas turbine recovers the energy ( The carbon emissions calculated based on these emissions should be included in the carbon footprint of the prevailing wind.

[0013] After entering the regenerator, the main air is used to burn the catalyst and is converted into high-temperature flue gas. During this process, the pressure energy of the main air is not lost; it is entirely transferred to the flue gas, becoming a crucial prerequisite for the flue gas to perform work in the flue gas turbine. Therefore, the carbon footprint of the main air (…) The carbon emissions should be included in the flue gas emissions. After the flue gas enters the waste heat boiler, it will generate steam through the superheating device. The carbon emissions converted from this steam should be included in the carbon footprint of the by-product steam.

[0014] (2) Carbon footprint of regenerated catalysts The catalyst acts as a heat carrier to transfer energy from the regenerator to the reactor. The energy required for the atomization and cracking reactions of the feedstock oil in the reactor is carried by the catalyst. The carbon emission source of this energy is the coking generated in the regenerator. Therefore, the carbon emission of the regenerated catalyst should be allocated according to the energy balance of the regenerator and the proportion of energy carried by the catalyst in the coking process.

[0015] (3) Steam carbon footprint The coking process of the catalyst in the regenerator generates excess heat. An external heat exchanger is typically installed to remove this excess heat. The external heat exchanger draws the catalyst out of the regenerator, extracts the heat, and then returns the cooled catalyst to the regenerator, thus achieving the purpose of removing excess heat and controlling the regenerator temperature. The heat exchanger recovers and utilizes the excess heat in the form of steam. Therefore, the carbon footprint of steam should be allocated to the carbon emissions of the coking process based on its proportion of heat consumption. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the absorption stabilization system of a catalytic cracking unit. Detailed Implementation

[0018] The carbon footprint of a regenerator can be calculated using the method proposed in this patent, as follows.

[0019] 1. Carbon emissions from regenerators The coke burned in the regenerator is not 100% carbon, but a mixture of highly hydrogen-poor hydrocarbons and heavy hydrocarbons that have not been stripped from the settling tank. Generally, it is estimated to have a carbon content of 91% to 94%. The carbon emissions from the coking process in the catalytic cracking unit can be calculated using the following formula:

[0020] In the formula: — Carbon emissions from regenerator coking, in tons; — Coke production rate of the catalytic cracking unit, in tons; —The average carbon content of coke from catalytic cracking units is generally taken as 92%; —The carbon oxidation rate during the coking process is generally taken as 98%.

[0021] 2. Regenerator Energy Balance The energy balance input of the regenerator is the coke heat, and the energy balance output includes three parts: energy carried by the catalyst, energy carried by the flue gas, and energy generated by the steam.

[0022] 1) Coke combustion heat. Coke combustion heat is generally calculated from the heat of coke combustion. The heat released by coke combustion is generally calculated by adding the heat of combustion of each element that makes up the coke. When the coke contains 92% carbon and 8% hydrogen, the heat of coke combustion can be calculated as 39.76 MJ / kg.

[0023] 2) Heat generated by steam. This can be calculated from the steam production rate and steam vaporization enthalpy of the regeneration process, using the following formula:

[0024] In the formula: —Steam heat production, GJ / hr; —Steam output of the heat exchanger, t / h; —Enthalpy of vaporization of the produced steam, MJ / t.

[0025] 3) Heat carried by the catalyst: This is calculated based on the catalyst circulation rate and the temperatures entering and exiting the regenerator, using the following formula:

[0026] In the formula: —The catalyst carries heat, GJ / hr; —Catalyst circulation rate, t / h; —The average specific heat capacity of the catalyst between T2 and T3, kJ / (kg·℃), generally calculated as 1.097 kJ / (kg·℃); —Temperature of the regenerated catalyst, °C; —Temperature of the catalyst to be generated, °C.

[0027] 4) Heat carried by the flue gas. This is calculated based on the main air volume, the temperature of the main air entering the regenerator, and the temperature of the flue gas exiting the regenerator, using the following formula:

[0028] In the formula: —The flue gas carries heat, in GJ / hr; —Main airflow, m 3 / h; —Specific heat capacity of air, 1.08 kJ / (kg·℃); T 3—Regenerator flue gas outlet temperature, °C; —Temperature of main air entering the regenerator, °C; 3. Carbon emission distribution of regenerators Carbon emissions from the regenerator are allocated based on its energy balance, including catalyst carbon emissions, steam carbon emissions, and flue gas carbon emissions, as shown in the following formula:

[0029]

[0030]

[0031] In the formula: —Carbon emissions from energy distribution carried by catalysts, kgCO2 / hr; — Carbon emissions from energy distribution carried by flue gas, tCO2 / hr; — Carbon emissions from the distribution of steam energy, tCO2 / hr; Meanwhile, the heat recovered by the flue gas turbine and waste heat boiler comes from the regenerator, therefore their calculated carbon emissions are related to the regenerator, as shown in the following formula:

[0032]

[0033] In the formula: — Carbon emissions converted from energy recovered by flue gas turbines, kgCO2 / hr; —The energy released by the flue gas in the flue gas turbine, MJ / hr; — Carbon emissions converted from energy recovered by waste heat boilers, kgCO2 / hr; —Energy released by flue gas in a waste heat boiler, MJ / hr; 4. Carbon footprint of flue gas The main air required for regenerator coke combustion is obtained by compressing air from a main air fan, which is driven by a flue gas turbine and an electric motor (or steam turbine): the flue gas turbine partially drives the main air fan, replaces part of the rotational energy consumption, and the remaining energy is provided by the electric motor. Therefore, the process of obtaining the main air consumes energy from both the electric motor and the flue gas turbine, and its carbon footprint is as follows:

[0034] In the formula; —The carbon footprint of the prevailing wind, kgCO2 / Nm3; — Carbon emissions generated by the energy consumption (electricity) of the electric motor driving the main fan, kgCO2 / hr; Since the pressure energy of the main air is entirely transferred to the flue gas, the carbon footprint of the main air should be included in the carbon footprint of the flue gas; simultaneously, after exiting the waste heat boiler, the flue gas enters the desulfurization and denitrification unit for treatment, and the carbon emissions from this process... It should also be included in the flue gas carbon footprint, from which the flue gas carbon footprint can be obtained, as shown in the following formula:

[0035] In the formula: — Carbon footprint of flue gas, tCO2 / Nm3; — Carbon emissions from flue gas desulfurization and denitrification processes; kgCO2 / hr.

[0036] 5. Catalyst and Steam Carbon Footprint The carbon footprint of the catalyst and steam can be calculated from the carbon emissions of the catalyst and steam distribution within the regenerator, as shown in the following formulas:

[0037]

[0038] In the formula: —Steam carbon footprint, kgCO2 / t; —Catalyst carbon footprint, kgCO2 / t.

Claims

1. A method for evaluating the carbon footprint of a regenerator in a catalytic cracking unit, characterized in that: According to the energy balance of the regenerator, the carbon emission of the decoking process is distributed by the energy carried by the catalyst ( ), the energy carried by the flue gas ( ) and the energy of the produced steam ( ).

2. A method for evaluating the carbon footprint of a regenerator in a catalytic cracking unit, characterized in that: According to flue gas in flue gas turbine recovery energy ( ) and waste heat boiler recovery energy ( ) calculation flue gas in flue gas turbine offset carbon emissions ( ) and waste heat boiler offset carbon emissions ( ).

3. A method for evaluating the carbon footprint of a regenerator in a catalytic cracking unit, characterized in that: The main air carbon footprint ( ) is calculated by the carbon emission of the power consumption of the main air fan motor ( ) and the carbon offset of the flue gas turbine ( ). The main air carbon footprint ( ) is fully included in the flue gas carbon footprint.

4. A method for evaluating the carbon footprint of a regenerator in a catalytic cracking unit, characterized in that: The flue gas carbon footprint is calculated from the main air carbon footprint emissions ( ), flue gas distribution regenerator carbon emissions ( ), flue gas turbine offset carbon emissions ( ), waste heat boiler offset carbon emissions ( ), and flue gas desulfurization and denitrification link carbon emissions ( ).

5. A method for evaluating the carbon footprint of a regenerator in a catalytic cracking unit, characterized in that: The catalyst carbon footprint (C) is calculated from the catalyst distribution regenerator carbon emissions (Cdr) and the catalyst circulation quantity (Cc). ​​​ 6. A method for evaluating the carbon footprint of a regenerator in a catalytic cracking unit, characterized in that: Steam carbon footprint ( The carbon emissions from the steam distribution regenerator ( Waste heat boiler carbon emission deduction ) and steam production ( )calculate.

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