Patent Application
20210087473
The present invention relates to a process for converting the waste plastic along with the petroleum residue feedstock in a Delayed Coker unit employed in refineries.
Issue of waste plastic disposal has been a grave concern worldwide and in India in particular, with staggering 6 million tons of waste plastic being generated in India every year. Use of disposal methods such as landfill suffer from issues like groundwater contamination, land use pattern etc. incineration of plastics cause air pollution hampering the health of flora and fauna. Specifically, there is no effective recycling or processing option for metal containing Polyethylene and Polypropylene multi-layer plastics films. With the increased awareness of public regarding cleanliness of public places and waste segregation, it is now becoming increasingly feasible to collect and segregate waste plastics from rest of the waste materials. It is also observed that the liquid and gaseous products of thermal cracking of waste plastics do not meet the complete specifications of end products like gasoline, diesel etc. and require further treatment. This aspect makes a petroleum refinery ideal location for waste plastic conversion since the products of plastic conversion can be fed to the product separation and treatment units along with other hydrocarbon products generated from crude oil. Using the present invention, the collected waste plastics can be co-processed along with residue hydrocarbons in a Delayed Coker Unit and can be converted to useful lighter products.
PCT application WO 95/14069 describes a process for disposal of waste plastics in Delayed Coker process. In said process, the waste plastic is dissolved in a highly aromatic solvent such as furfural in a vessel and the plastic solution is mixed with the feedstock which is processed in Delayed Coker drum in the normal processing route.
US Patent No. 2018/0201847 describes a process for conversion of waste plastics through hydro-treating route. Waste plastics are mixed with heavy crudes and vacuum residues and the resultant mixture is hydro-processed to produce lighter hydrocarbon products.
U.S. Pat. No. 4,118,281 describes a process wherein the waste plastic material is ground into a slurry form and is mixed with the feedstock being processed in the normal process scheme of Delayed Coker unit, passing through fractionator, furnace and coke drums.
It can be seen that in the prior art schemes, the waste plastic material are subjected to size reduction or dissolution in reagents or melting and is routed through furnace and into coke drums thereafter. While these schemes may be advantageous in certain categories of plastics, these may not be suitable for all types of plastics like metal additized plastics. In cases of a mixture of waste plastics containing different types of plastics of varying melting points and metal contents, there is a possibility of non-uniform mixing of components as well as enhanced coke formation inside the Delayed Coker furnace tubes. Metallic components may separate from the rest of the matrix and get deposited in the tube walls of Delayed Coker furnace, or also act as active sites for coke formation inside furnace tubes. Further in schemes where polymer is melted and mixed with feedstock, there can be issues of high viscosity and density difference of polymer melts compared to hydrocarbon feedstocks. This variation in the rheological properties of the hydrocarbon feedstock & polymer melt can cause variation in flow pattern of the two inside the furnace tubes of the Delayed Coker and can cause choking and coking problems of furnace tubes. It is therefore desired to have a process and apparatus addressing the concerns of the prior art.
It is the primary objective of the present invention is to provide the thermal cracking process to convert low value plastic waste material into higher value lighter distillate products in a Delayed Coker unit.
It is the further objective of the present invention is to provide the process for co-conversion of waste plastics along with petroleum residues employing thermal cracking into valuable lighter distillate products.
It is the further objective of the present invention is to provide unique hardware system/apparatus and method to process waste plastics in Delayed Coker unit.
Accordingly, the present invention provides a method for thermal cracking of waste plastic into lighter distillate products.
In another feature of the present invention, the waste plastics are supplied from the plastic feeder vessel to the coke drum by using a conveyer such as screw conveyer.
In another preferred feature of the present invention, the waste plastic material is kept in the plastic feeder vessel in the molten form by application of heat and is supplied to the coke drum in liquid form.
In yet another feature of the present invention, the waste plastic transport from the waste plastic supply vessel to the coke drums is carried out by means selected from pneumatic transport, extrusion or melt injection or combination thereof.
In yet another feature of the present invention, the waste plastic is selected from the group consisting of polystyrene, polypropylene, polyethylene, PET including metal additized multilayer plastics or combination thereof.
In yet another feature of the present invention, the physical form of waste plastic is selected from the group consisting of granules, powder, crushed chunks, slurry, melt or combination thereof.
In another feature of the present invention, percentage of waste plastic in comparison with the hydrocarbon feedstock supplied is in the range of 0.01 to 50 wt % preferably between 0.5 to 10 wt %.
In one feature of the present invention, the hydrocarbon feedstock is selected from crude oil, vacuum residue, atmospheric residue, deasphalted pitch, shale oil, coal tar, clarified oil, residual oils, heavy waxy distillates, foots oil, slop oil or mixture thereof.
The process as claimed in claim 1, wherein the conradson carbon residue content of the hydrocarbon feedstock is in the range of 3 to 30 wt % and density in the range of 0.95 to 1.08 g/cc.
In another feature of the present invention, thermal cracking section of the process is operated at a higher severity with desired operating temperature ranging from 470 to 520° C., preferably between 480° C. to 500° C. and desired operating pressure ranging from 0.5 to 5 Kg/cm2 (g) preferably between 0.6 to 3 Kg/cm2 (g).
In yet another feature of the present invention, the secondary feed in step (ii) is heated at a temperature in the range of 470 to 520° C.
In further feature of the present invention, cycle time of the coking and decoking cycles of the coke drums are more than 10 hr.
In another feature of the present invention, product vapors from the coke drums are routed to the main fractionator column for separation into different product fractions like Light Coker Gasoil, Heavy Coker Gasoil, and Coker Fuel Oil.
In further feature of the present invention, the vapor fractions are sent to the Gas concentration and separation section for separation of fuel gas, LPG and naphtha.
In another feature of the present invention, comprises a system for conversion of a waste plastic into light distillate products, the system including coke drums in the delayed coking process, fractionators column connected to the coke drums, and a add-on section(s)/supply vessel(s).
The present invention also provides an apparatus for conversion of a waste plastic into light distillate products, the system comprising:
In one feature of the present invention, the waste plastic supply vessel is located at higher elevation than coke drums to enable smooth flow of plastics to the coke drums.
In another feature of the present invention, the waste plastic is conveyed into the waste plastic supply vessel from another unloading vessel located at lower elevation compared to the waste plastic supply vessel through pneumatic transport or through conveyer belts.
In yet another feature of the present invention, the waste plastic from waste plastic supply vessel is conveyed to Coke Drums by means of either pneumatic transport, screw feeder, melt injection or combination of both.
In yet another feature of the present invention, the waste plastic supply vessel has facility for rousing gas injection and purging.
In yet another feature of the present invention, the waste plastic supply vessel optionally has facility for heating and melting of waste plastics.
In yet another feature of the present invention, the waste plastic supply rate from the waste plastic supply vessel is controlled by means of rotary airlock valve or pump.
In yet another feature of the present invention, the waste plastic supply vessel is kept under pressure higher than the coke drums, controlled by means of pressure control valve, in the range of 0.1 to 1 Kg/cm2g.
The present invention also provides an apparatus for conversion of a waste plastic into light distillate products, the system comprising:
In one feature of the present invention, the waste plastic supply vessel (13, 22, 52, 81, 108, 207) is located at higher elevation than coke drums to enable smooth flow of plastics to the coke drums.
In another feature of the present invention, the waste plastic is conveyed into the waste plastic supply vessel (13, 22, 52, 81, 108, 207) from another unloading vessel (71) located at lower elevation compared to the waste plastic supply vessel through pneumatic transport or through conveyer belts.
In yet another feature of the present invention, the waste plastic from waste plastic supply vessel (13, 22, 52, 81, 108, 207) is conveyed to Coke Drums by means of either pneumatic transport, screw feeder, melt injection or combination of both.
In yet another feature of the present invention, the waste plastic supply vessel (13, 22, 52, 81) has facility for rousing gas injection and purging.
In yet another feature of the present invention, the waste plastic supply vessel (108, 207) optionally has facility for heating and melting of waste plastics.
In yet another feature of the present invention, the waste plastic supply rate from the waste plastic supply vessel (13, 22, 52, 81) is controlled by means of rotary airlock valve or pump.
In yet another feature of the present invention, the waste plastic supply vessel (13, 22, 52, 81, 108, 207) is kept under pressure higher than the coke drums, controlled by means of pressure control valve, in the range of 0.1 to 1 Kg/cm2g.
Accordingly, present invention relates to a process to convert low value plastic waste material into higher value lighter distillate products like Fuel gas, LPG, naphtha, Light Coker Gasoil (LCGO), Heavy Coker Gasoil (HCGO) and Coker Fuel Oil (CFO) etc. along with solid petroleum coke by thermally cracking the same in a Delayed Coker unit along with hydrocarbon feedstock.
In detail, the invented process employs a unique process hardware scheme to feed the waste plastic into the coke drums directly without impacting the operation of other critical hardware like Furnace, which is susceptible to fouling, if there is impurities like metals, particles etc. in the feedstock being heated. The crushed waste plastic material is loaded into a fluidized feeder vessel and is supplied pneumatically to the coke drums through pneumatic conveying mechanism after the drum heating step is completed. Inside the coke drum, it undergoes co-conversion along with the hot petroleum residue stream which is being supplied from the bottom of the coke drum.
Lighter distillates generated while thermal co-conversion in the vapor form inside the coke drum gets mixed with product vapors generated from thermal cracking of hydrocarbon feedstock and the combined product vapor is then routed to the main fractionator column to separate into desired liquid product fractions like light coke gasoil, heavy coke gasoil and coke fuel oil. The off-gases from the fractionator column overhead section are routed to the GASCON section for separation of naphtha, Fuel gas and LPG. The residue coke materials produced during the conversion of waste plastic will be deposited along with solid petroleum coke formed inside the coke drum due to thermal cracking of hydrocarbon feedstock. The metals in the waste plastics are mostly not in organo-metallic form and therefore are deposited preferentially in solid petroleum coke inside coke drum.
Feedstock:
The liquid hydrocarbon feedstock to be used in the process is selected from heavy hydrocarbon feedstocks like reduced crude oil, vacuum residue, atmospheric residue, deasphalted pitch, shale oil, coal tar, clarified oil, residual oils, heavy waxy distillates, foots oil, slop oil or blends of such hydrocarbons. The Conradson carbon residue content of the feedstock is above 3 wt % and minimum density of 0.95 g/cc.
Waste Plastic:
Plastics are macromolecules, formed by polymerization and having the ability to be shaped by application of reasonable amount of heat and pressure or another form of forces. Plastic is a generic term for a wide range of polymers produced using highly refined fractions of crude oil, or chemicals derived from crude oil, known as monomers. Polymers are formed by the reaction of these monomers, which results in chain lengths of tens or hundreds of thousands of carbon atoms. Some polymers also contain oxygen (e.g. polyethylene terephthalate (PET)), whereas others contain chlorine (polyvinyl chloride (PVC)). Due to its non-biodegradable nature, the
plastic waste contributes significantly to the problem of waste management.
Plastics, depending upon their physical properties may be classified into thermoplastic or thermosetting plastic materials.
In one feature of the present invention, the waste plastics are supplied from the plastic feeder vessel to the coke drum by using a conveyer such as screw conveyer.
In another feature of the present invention, the waste plastic material is kept in the plastic feeder vessel in the molten form by application of heat and is supplied to the coke drum in liquid form.
In yet another feature of the invention, the waste plastics used for processing in the process of present invention can be in crushed form or as lumps which can be transported through other means like conveyer belts.
Process Conditions:
Reactor drums in the thermal cracking section of the process may be operated at a higher severity with desired operating temperature ranging from 470 to 520° C., preferably between 480° C. to 500° C. and desired operating pressure ranging from 0.5 to 5 Kg/cm2 (g) preferably between 0.6 to 3 Kg/cm2 (g). The cycle time of the coking and decoking cycles of the coke drums are kept more than 10 hr. The waste plastic material can be fed to the coke drum such as the percentage of waste plastic in comparison with the hydrocarbon feedstock supplied is in the range of 0.01 to 50 wt % preferably between 0.5 to 10 wt %.
Process Description:
The process of the present invention is exemplified by, but not limited to
The embodiment of the process of the present invention is exemplified by, but not limited to
One embodiment of the invention depicting plastic processing hardware and process is provided in
In another embodiment of invention depicting the plastic processing hardware and process is provided in
In yet another embodiment of the invention depicting plastic processing hardware and process is provided in
The process of present invention is exemplified by following non-limiting examples.
Vacuum reside feedstock was arranged from petroleum refinery and characterization was carried out. The properties of the vacuum residue feedstock are provided in Table-1.
Experiments conducted in Micro-Coker unit with waste granules of LDPE (Low Density Polyethylene), HDPE (High Density Polyethylene), Mix Plastic and the vacuum residue. The mixing of the waste plastics and the vacuum residue feedstock was inside the Micro-Coker reactor. The operating conditions of the reaction section maintained for the experiments are provided in Table-2.
The product yields obtained in different experiments by co-processing of plastics with vacuum residue are provided in Table-3.
It can be seen from the experimental data provided in Table-3 that the waste plastics have converted to gaseous and liquid fractions while co-processing.
Further, experiments were carried out using vacuum residue feedstock of Table-1 and multilayer metal additized waste plastic granules with properties provided in Table-4, in a Delayed Coker pilot plant of 1 barrel per day capacity.
Experimental conditions are provided in Table-5. Waste plastic granules are directly supplied to the Coke Drum bypassing the furnace, where it cracks to lighter hydrocarbon products.
Two experiments were carried out—with and without dosing of waste plastic to the Drum. The results of experiments are provided in Table-6. It can be seen that the additionally input waste plastic has converted to different product fractions as can be seen from the Kg/cycle of product formation from waste plastic.
A comparison of coke properties are provided in Table-7. It can be seen that the metal content in the waste plastic has deposited in the coke which is formed during the Delayed Coking reaction and therefore the ash content has increased. The liquid products are devoid of any additional metal due to waste plastic processing.
The following are the technical advantages of the present invention over the prior art as disclosed above:
| Number | Date | Country | Kind |
|---|---|---|---|
| 201921038366 | Sep 2019 | IN | national |
