Method for evaluating carbon footprint of absorption and stabilization system product in oil refining process

Abstract

The invention provides a method for evaluating carbon footprint of an absorption stabilization system product in an oil refining process, which comprises the following steps of: reasonably distributing carbon emission of the product according to an energy condition, and carrying out iterative solution on circulating materials such as desorbed gas, a supplementary absorbent and absorption tower bottom oil; comprising the following steps: replacing an initial value (or a value calculated in the previous step) of a condensed oil tank evaluation process with an absorption tower bottom oil carbon footprint calculated by an absorption tower and a desorption gas carbon footprint calculated by a desorption tower by applying an iteration method, and recalculating to obtain a condensed oil tank liquid phase product carbon footprint; replacing the initial value (or the value calculated in the previous step) in the calculation process of the absorption tower with the carbon footprint of the supplementary absorbent calculated by the stabilization tower, and recalculating to obtain the carbon footprint of the absorption tower bottom oil; the iterative calculation result is used for calculating the desorption tower and the stabilization tower again, and a desorption gas carbon footprint and a supplementary absorbent carbon footprint are obtained; and repeatedly executing the process until the data result converges.

Description

Technical Field

[0001] This invention relates to the field of oil refining technology, and in particular to a method for evaluating the carbon footprint of products from an absorption stabilization system in an oil refining process. Background Technology

[0002] Product carbon footprint assessment is an assessment of 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 usually evaluated using carbon dioxide mass equivalent (CO2e).

[0003] In oil refining processes, absorption and stabilization systems are typically found in catalytic cracking or delayed coking units. Their function is usually to separate rich gas and crude gasoline from fractionation towers into dry gas, liquefied petroleum gas (LPG), and stabilized gasoline. Currently, a four-tower process consisting of an absorber, reabsorber, desorber, and stabilizer is commonly used. Figure 1 As shown.

[0004] The rich gas, the desorbed gas from the top of the desorber, and the bottom oil from the absorber come into contact in the condensate tank. The gas phase (condensate) from the condensate tank enters the bottom of the absorber, where it comes into countercurrent contact with the crude gasoline and supplementary absorbent entering from the top of the tower. The C3 and higher components in the condensate are absorbed. The bottom absorbent oil enters the condensate tank, while the top gas phase enters the reabsorption tower, where it comes into countercurrent contact with the lean absorbent oil, further absorbing the heavier components. The top gas from the reabsorption tower is dry gas, and the bottom gas, rich absorbent oil, returns to the main fractionation tower. The liquid phase from the condensate tank enters the desorber, where heat is supplied to the bottom to decompose and remove the C2 and lower components. The top desorbed gas returns to the condensate tank, and the bottom gas yields de-ethaned gasoline. The de-ethaned gasoline enters the stabilization tower for further separation, yielding top liquefied petroleum gas (LPG) and bottom stabilized gasoline. A portion of the bottom gasoline is cooled and used as supplementary absorbent in the absorber. As can be seen from the above process, the dry gas produced by the absorption stabilization system is produced from the top of the reabsorption tower, while liquefied petroleum gas and stabilized gasoline are produced from the top and bottom of the stabilization tower, respectively.

[0005] In this process, the desorption tower and stabilization tower typically consume a certain amount of energy as a heat source for the reboiler at the bottom of the tower, which is the main source of carbon emissions. When conducting a carbon footprint assessment of the product, it is necessary to allocate the carbon emissions from the bottom of the aforementioned fractionation towers to the product.

[0006] The following issues exist in evaluating the carbon footprint of absorption stabilization systems: First, the carbon emissions of products are allocated for fractionation processes such as desorption towers and stabilization towers, which have high energy consumption and large carbon emissions; second, although the phase equilibrium process of rich gas, desorbed gas, and absorbent oil in the condensate tank does not consume energy or generate carbon emissions, energy exchange occurs during mass transfer and should be calculated according to energy status; third, the carbon footprint data for material circulation processes such as desorbed gas, replenished absorbent, and absorbent bottom oil are continuously iterated and solved based on the circulation process. Summary of the Invention

[0007] In view of this, the present invention provides a method for evaluating the carbon footprint of products from an absorption stabilization system. While rationally allocating carbon emissions from fractionation tower products, an iterative method is used to solve the material circulation processes such as desorbed gas, replenished absorbent, and bottom oil of the absorption tower.

[0008] (1) Carbon footprint of condensate tank products

[0009] The condensate tank is used to balance the rich gas, desorbed gas, and bottom oil of the absorber to obtain the gas phase feed to the absorber and condensate. This process does not consume or produce energy, and its carbon emissions are 0.

[0010] The composition of the rich gas feed shows that the gas-liquid balance process in the condensing tank is mainly the entry of the heavy components of the rich gas into the liquid phase, while the changes in the light components are not significant. Therefore, it can be considered that the carbon footprint of the gas phase product of the condensing tank is the same as that of the rich gas, and the carbon footprint of the liquid phase product can be calculated by process additivity.

[0011] CF g,ct =CF g,r

[0012]

[0013] Where: CF g,ct —The carbon footprint of vapor products from condensed oil tanks

[0014] CF g,r —The carbon footprint of the rich gas feedstock;

[0015] CF l,ct —The carbon footprint of liquid products from condensed oil tanks

[0016] F g,des F l,abs F l,ct — Desorber top gas phase product, absorption tower bottom oil, and condensate flow rate;

[0017] F g,r F g,ct —Raw material rich gas, gas phase flow rate of condensate tank.

[0018] CF g,des CF l,abs —Gas phase products at the top of the desorption tower and oil and carbon footprint at the bottom of the absorption tower.

[0019] (2) Carbon footprint of absorption towers and reabsorption towers

[0020] The main function of the absorber is to dissolve the heavy components in the rich gas into the crude gasoline. This process releases heat, necessitating an intermediate heat recovery section to remove this heat. Since this heat is typically carried away by the circulating water and not utilized, it cannot be used to offset the carbon footprint of the absorption process products. If we ignore the carbon emissions from the circulating water consumption process, the heavy components in the gaseous feed to the absorber are absorbed by the absorbent oil, and the light components are the overhead gas, whose carbon footprint can be considered the same as the feed gas phase. The carbon footprint of the absorber bottom liquid can be calculated based on the flow rates and carbon footprints of the crude gasoline and the supplementary absorbent, using the process additivity, as shown in the following formula:

[0021]

[0022] Where: CF l,abs —Oil and carbon footprint at the bottom of the absorption tower

[0023] F cgas F sabs —Crude gasoline and supplement absorbent flow rates;

[0024] CF cgas CF sabs —The carbon footprint of crude gasoline and supplemental absorbents

[0025] F g,abs F l,abs —Flow rates of gaseous and liquid products in the absorption tower

[0026] Similarly, the reabsorption tower follows the same rule.

[0027] (3) Carbon footprint of desorption tower

[0028] The desorption tower primarily decomposes and extracts light components (C2 and above) from the condensed oil. The desorption process requires endothermic heat; therefore, the desorption tower is equipped with multiple reboilers. Its carbon emissions can be calculated from the desorption tower's heat load. According to the energy balance of the desorption tower, the energy of the desorbed gas and deethaned gasoline is higher than that of the feed condensed oil. Therefore, the carbon footprint of the desorbed gas and deethaned gasoline can be calculated using the energy allocation method, as shown in the following formula:

[0029] CF p,des =CF l,ct +(h p,des -h f,des )·EF des

[0030] Where: CF p,des — Carbon footprint of desorber products (bottom or top of the tower)

[0031] h p,des h f,des—Desorption tower product (bottom or top of tower), feed enthalpy, MJ / t;

[0032] EF des — Carbon emission factor per unit calorific value of desorption tower, kgCO2 / MJ;

[0033] (4) Carbon footprint of stabilization tower

[0034] Carbon emissions from a stabilized column can be calculated from the heat load of its bottom reboiler. The carbon footprints of the bottom and top products can be allocated to carbon emissions based on their respective energy gains, with the top product measured as gas-phase conditional energy.

[0035]

[0036] In the formula:

[0037] E D —The increase in energy of the top product compared to the feed under vapor phase conditions when exiting the fractionation tower;

[0038] D, L – Top product yield and top liquid reflux flow rate;

[0039] h D —Enthalpy value of the product at the top of the tower after condensation and cooling;

[0040] Q c —Top condenser load;

[0041] h F —Infeed enthalpy.

[0042] (5) Carbon footprint results

[0043] In the carbon footprint assessment of the absorption stabilization system, there are material cycles of desorbed gas-condensate tank-condensate oil-desorbed tower-desorbed gas and condensate gas-absorber-absorbate oil-condensate tank-condensate gas. A system model is constructed for calculation. Detailed Implementation

[0044] The carbon footprint of an absorption stabilization system product can be calculated using the method proposed in this patent, following the procedure below.

[0045] 1. Calculate the vapor flow rate of the condensate tank from the flow rates of rich gas, desorbed gas, and bottom oil of the absorber, and set the carbon footprint (CF) of the desorbed gas. g,des and the carbon footprint of the bottom oil of the absorber (CF) l,abs Initial values ​​were obtained, and the carbon footprint (CF) of condensed oil was calculated from the carbon footprint of gas-rich oil. l,ct ;

[0046] 2. Calculate the material balance of the absorbent tower based on the gas phase flow rates of the supplementary absorbent, crude gasoline, and condensate tank, and set the carbon footprint (CF) of the supplementary absorbent. sabsInitial values ​​were used, and the carbon footprint (CF) of the bottom oil in the absorber was calculated in conjunction with the carbon footprint of the crude gasoline. l,abs and the gas phase carbon footprint CF of the absorption tower g,abs The carbon footprint of the absorption tower in the gas phase is the carbon footprint of the dry gas product.

[0047] 3. Based on the material balance, energy balance, and carbon footprint of the desorption tower (CF) l,ct Calculate the carbon footprint (CF) of the desorbed gas g,des and the carbon footprint of deethaned gasoline CF l,des .

[0048] 4. Calculated based on material balance, energy balance, and carbon footprint (CF) of deethaned gasoline from the stabilizer tower. l,des Calculate the carbon footprint (CF) of liquefied petroleum gas g,stb and stable gasoline carbon footprint CF l,stb Among them, the stable gasoline carbon footprint is the supplementary absorbent carbon footprint CF sabs .

[0049] 5. Calculate the carbon footprint (CF) of the bottom oil of the absorber based on the absorber tower. l,abs The carbon footprint (CF) of the desorbed gas calculated by the desorber. g,des Substituting the initial values ​​(or the values ​​calculated in the previous step) into the condensate tank process, the carbon footprint (CF) of the condensate is obtained again. l,ct ;

[0050] 6. The carbon footprint (CF) of the supplementary absorbent calculated by the stabilizer tower. l,stb Substituting the initial values ​​(or previous calculation values) into the absorption tower calculation process, the carbon footprint CF at the bottom of the absorption tower is obtained again. l,ct ;

[0051] 7. Use the results of iterative calculations in steps 5 and 6 to calculate the desorption tower and stabilization tower, and re-obtain the carbon footprint (CF) of the desorbed gas. g,des and supplemental absorbent carbon footprint CF l,stb ;

[0052] 8. Repeat steps 5, 6, and 7 until the above data results converge. Attached Figure Description

[0053] Appendix Figure 1 Flow diagram of the absorption stabilization system of a catalytic cracking unit in a refinery.

[0054] Appendix Figure 2 Condensation Tank Flow Chart

[0055] Example 1

[0056] The process flow of the absorption stabilization system of a certain catalytic cracking unit is as follows: Figure 1 As shown, the desorption tower is equipped with an intermediate reboiler E-301C, a bottom reboiler E301A, and a bottom reboiler E301B.

[0057] After heat exchange between the deethane-removed gasoline at the bottom of the desorption tower and the stabilized gasoline, the gasoline is sent to the stabilization tower to separate liquefied petroleum gas (LPG) and stabilized gasoline products. The reboilers (E-304 / A, B) at the bottom of the stabilization tower are heated by the circulating oil from the second fractionation stage. The material balance of this absorption stabilization system is shown in Table 1.

[0058] Table 1 Material Balance of Absorption Stabilization System

[0059]

[0060] (1) Carbon footprint of absorption tower and reabsorption tower

[0061] The absorber has four intermediate heat recovery and reflux sections with reflux flow rates of 66 t / hr, 65 t / hr, 66 t / hr, and 115 t / hr, respectively. Taking the extraction and return temperatures as 5°C, the heat recovery can be calculated as (66 t / hr + 65 t / hr + 66 t / hr + 115 t / hr) × 2.2 MJ / (t·°C) × 5°C = 3432 MJ / hr. This heat is carried away by the circulating water and not utilized. If the carbon emissions from the circulating water consumption process are ignored, the heavy components in the absorber's gaseous feed are absorbed by the absorbent oil, and the light components become the absorbent gas, which has the same carbon footprint as the feed gas phase. The carbon footprint of the absorber bottom liquid can be calculated additively, i.e., based on the flow rates and carbon footprints of the crude gasoline and the supplementary absorbent. The same principle applies to the reabsorption tower.

[0062] (2) Carbon footprint of desorption tower

[0063] The intermediate reboiler E-301C of the desorption tower uses stable gasoline as a heat source, the bottom reboiler E301 / A of the desorption tower uses the reflux from the first section of fractionation as a heat source, and the bottom reboiler E301B of the desorption tower uses the lean absorption oil from fractionation as a heat source.

[0064] ① The temperature after passing through E301 is 141℃, therefore it can be calculated as the heat load of the desorption tower reboiler.

[0065] =50.23GJ / hr÷(260℃-130℃)×(260℃-141℃)=45.98GJ / hr

[0066] ② The heat exchange temperature of the lean absorbent oil is 194℃ to 98℃, and its heat load as the heat source for the desorption tower reboiler is...

[0067] =14.50GJ / hr÷(194℃-80℃)×(194℃-98℃)=12.21GJ / hr.

[0068] ③ The stable gasoline, used as an intermediate reboiler, has a heat exchange temperature ranging from 173℃ to 141℃. Simulations show its enthalpy values ​​are 668.13 MJ / t and 568.54 MJ / t, respectively. Therefore, its heat exchange load = (201.54 t / hr + 70 t / hr) × (668.13 MJ / t - 568.54 MJ / t) = 26.64 GJ / hr. Thus, the total input heat load to the desorption tower = 45.98 GJ / hr + 12.21 GJ / hr + 26.64 GJ / hr = 84.83 GJ / hr

[0069] With a feed condensate oil temperature of 47℃, a desorbed gas temperature of 52℃ at the top of the desorbed tower, and a deethaned gasoline temperature of 125℃ at the bottom of the tower, and a pressure of 1.4MPa, the simulated enthalpies are 106.37MJ / t, 428.17MJ / t, and 250.57MJ / t, respectively. The energy balance of the desorbed tower is shown in Table 2.

[0070] Table 2 Energy Balance Sheet of Desorption Tower

[0071]

[0072] Carbon emissions from heat consumption in desorption towers

[0073] =(45.98GJ / hr+12.21GJ / hr+26.64GJ / hr)×88.52kgCO2 / GJ=7509.15kgCO2 / hr.

[0074] Energy increase of desorbed gas compared to feed condensed oil

[0075] =46.13t / hr×(434.33MJ / t-106.37MJ / t)=15128.79MJ / hr

[0076] Energy gain of deethaned gasoline compared to feedstock condensate

[0077] =360.93t / hr×(279.57MJ / t-106.37MJ / t)=62513.08MJ / hr

[0078] According to the energy allocation method, the unbalanced terms in the energy balance calculation are allocated, and the increase in carbon footprint of desorbed gas compared with condensed oil is 7509.15kgCO2 / hr × 15128.79MJ / hr ÷ (15128.79MJ / hr + 62513.08MJ / hr) ÷ 46.13t / hr = 31.72kgCO2 / t.

[0079] The increase in carbon footprint of deethaned gasoline compared to condensed gasoline

[0080] =7509.15kgCO2 / hr×62513.08MJ / hr÷(15128.79MJ / hr+62513.08MJ / hr)÷360.93t / hr=16.75kgCO2 / t.

[0081] (3) Carbon footprint of condensate tanks

[0082] The condensate tank is used to achieve phase equilibrium treatment of rich gas, desorbed gas, and bottom oil from the absorber, resulting in the absorber gaseous feed and condensate. This process consumes and produces no energy, and its carbon emissions are zero. In the gas-liquid equilibrium process of the condensate tank, the heavier components of the rich gas mainly enter the liquid phase, while the changes in the lighter components are not significant. Therefore, the carbon footprint of the condensate tank's gaseous product can be considered the same as that of the rich gas, and its liquid-phase product carbon footprint can be calculated using process additivity.

[0083] (4) Carbon footprint of stabilization tower

[0084] The heat load of the reboiler at the bottom of the stabilizer is 72.87 GJ / hr, which is approximately equivalent to carbon emissions.

[0085] =72.87GJ / hr×88.52kgCO2 / GJ=6450.45kgCO2 / hr.

[0086] The top temperature of the tower is 63℃, the reflux flow rate is 152t / hr, the bottom temperature is 173℃, and the feed temperature of the deethaned gasoline is 113℃. The enthalpies of the top vapor phase, feed, and bottom material can be simulated as 431.70 MJ / t, 283.99 MJ / t, and 388.68 MJ / t, respectively. The enthalpy of the top vapor phase after condensation is 168.70 MJ / t. Therefore, the heat of condensation of the top vapor phase...

[0087] = (152t / hr + 93.4t / hr) × (431.70MJ / t - 168.70MJ / t) = 64.54GJ / hr. The energy balance of the distillation tower can be calculated as shown in Table 3.

[0088] Table 3 Energy Balance of Stabilizer Tower

[0089]

[0090]

[0091] The energy increase when the top product of the stabilizer column exits the fractionation column under gas phase conditions.

[0092] =93.4t / hr×[168.70MJ / t+64.54GJ / hr×1000MJ / GJ÷(152t / hr+93.4t / hr)-283.99MJ / t]=13781.27MJ / hr

[0093] The increase in energy of the product at the bottom of the tower = (201.54t / hr + 66t / hr) × (358.68MJ / t - 283.99MJ / t) = 19982.56MJ / hr.

[0094] The combined energy increase of the two mentioned above is 13781.27 MJ / hr + 19982.56 MJ / hr = 33763.83 MJ / hr. The heat recovery of the fractionation column from the reflux liquid phase of 152 t / hr is 152 t / hr × (431.70 MJ / t - 168.70 MJ / t) ÷ 1000 MJ / GJ = 39.98 GJ / hr. This portion of energy is not carried by the product and can be allocated according to the energy acquisition of the product. If the carbon emissions from the cooling process at the top of the column are ignored, the carbon footprint of the product at the top of the column increases compared to the carbon footprint of the feed.

[0095] =6450.45kgCO2 / hr×13781.27MJ / hr÷(13781.27MJ / hr+19982.56MJ / hr)÷93.4t / hr=28.19kgCO2 / hr

[0096] The carbon footprint of the bottom product is higher than that of the feed.

[0097] =6450.45kgCO2 / hr×19982.56MJ / hr÷(13781.27MJ / hr+19982.56MJ / hr)÷

[0098] (201.54t / hr + 66.00t / hr)

[0099] = 14.27 kg CO2 / hr.

[0100] (5) Carbon footprint results

[0101] In the carbon footprint evaluation of the absorption stabilization system, there are material cycles of desorbed gas-condensate tank-condensate oil-desorbed tower-desorbed gas and condensate gas-absorber-absorbate oil-condensate tank-condensate gas. Therefore, iterative calculations need to be performed based on the initial values. The converged results are shown in Table 4.

[0102] Table 4. Calculation results of carbon footprint of a certain absorption stabilization system product.

[0103]

[0104] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for evaluating the carbon footprint of products from an absorption stabilization system in an oil refining process, characterized in that: The method is applicable to the absorption stabilization process in catalytic cracking and delayed coking units, and can be used as a reference for light hydrocarbon recovery processes; 2. A method for evaluating the carbon footprint of products from an absorption stabilization system in an oil refining process, characterized in that: Calculate the vapor flow rate of the condensate tank based on the flow rates of rich gas, desorbed gas, and bottom oil of the absorber, and set the carbon footprint of the desorbed gas. And the carbon footprint at the bottom of the absorption tower Initial values ​​are used, and the carbon footprint of condensed oil is calculated from the carbon footprint of gas-rich oil. ; 3. A method for evaluating the carbon footprint of products from an absorption stabilization system in an oil refining process, characterized in that: The material balance of the absorber is calculated based on the gas phase flow rates of the supplementary absorbent, crude gasoline, and condensate tank, and the carbon footprint of the supplementary absorbent is set. Initial values ​​were used, and the carbon footprint of the bottom oil in the absorber was calculated in conjunction with the carbon footprint of the crude gasoline. and the gas phase carbon footprint of the absorption tower The carbon footprint of the absorption tower in the gas phase is the carbon footprint of the dry gas product.

4. A method for evaluating the carbon footprint of products from an absorption stabilization system in an oil refining process, characterized in that: Material balance, energy balance, and carbon footprint of condensed oil from the desorption tower Calculate the carbon footprint of desorbed gas carbon footprint of deethaned gasoline .

5. A method for evaluating the carbon footprint of products from an absorption stabilization system in an oil refining process, characterized in that: The results of stabilizer tower material balance, energy balance, and carbon footprint of deethaned gasoline. Calculating the carbon footprint of liquefied petroleum gas and stable gasoline carbon footprint Among them, the carbon footprint of stable gasoline is the carbon footprint of supplemental absorbent. .

6. As described in claims 3, 4, and 5, the calculated bottom oil carbon footprint of the absorber tower is... Carbon footprint of desorbed gas calculated by desorber Recalculate the carbon footprint of the condensate oil using the initial values ​​(or previous calculation values) from the condensate tank process. The carbon footprint of the supplemental absorbent calculated for the stabilizer tower. Substitute the initial values ​​of the absorber tower (or the values ​​calculated in the previous step) to recalculate the carbon footprint at the bottom of the absorber tower. The desorption tower and stabilization tower were recalculated using the above iterative calculation results to obtain the carbon footprint of the desorbed gas. and supplemental absorbent carbon footprint Repeat the above process until the data results converge.

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