Patent Application
20250115813
The present disclosure relates to a method for treating hydrocarbon effluent from hydrothermal liquification of plastic waste. In examples, the process and system as described relate to treating a hydrocarbon effluent stream generated in a hydrothermal liquification of plastic waste.
The plastics pyrolysis oil obtained from various plastics recycling processes contains multitude of impurities. Some impurities may include silicon, chlorides, metals, heteroatoms, etc. The impurities often are present in elevated levels and can be detrimental to downstream units such as steam cracking units. Accordingly, the impurities are typically removed. Processes that are generally used to remove impurities include adsorption or hydrogen addition to produce clean products.
Hydrothermal liquefaction (HTL) is a thermochemical process that can convert biomass or organic waste into a liquid bio-oil under high temperature and pressure. This process is similar to the geological processes that create fossil fuels but takes place in a much shorter time frame. During the HTL process, a plastic waste which may be biomass is mixed with water and then heated to temperatures ranging from 150° C. to 600B° C. in a pressurized reactor. The high pressure and temperature conditions break down the complex organic molecules in the biomass into smaller molecules, forming a bio-oil that can be separated from the remaining solids and water. The resulting plastic-oil can be used as a renewable fuel source for transportation or further processed into other products.
HTL has several advantages over other biofuels production processes. For example, HTL process a wide range of feedstocks, including agricultural waste, forestry residue, and even algae. HTL can also be used to convert plastic waste to plastic oil into a liquid fuel. The process is like that used in pyrolysis process, but with some differences in the operating conditions and the use of supercritical water.
Most refiners use separate di-olefins reactor to saturate dienes in the waste plastics oil. Waste plastics oil is associated with high diene content in the feed and as result it polymerizes at elevated temperatures. A dedicated diolefins saturation reactor is required at temperature operating at no more than 210° C. to ensure that these highly reactive species are removed from the feed before polymerization can take place.
However, there are also some challenges to using HTL for plastic waste. For example, some types of plastics may produce toxic byproducts during HTL, and the process may require additional energy to remove contaminants from the liquid product. Additionally, the process may not be economically feasible for small-scale operations due to the high capital and operating costs of the reactor.
In examples, disclosed herein an HTL process may be used to convert plastic waste into plastic oils and other valuable products.
In examples, the process may be used to cover a wide range of plastic recycled oil using hydrothermal liquefaction into polished hydrocarbons by hydro-processing. In examples, the conversion may lead to 100% or close to 100% plastic waste conversion into hydrocarbons.
In examples, the process as described may produce steam cracker feedstock or clean fuel products. In examples, the process may involve a hydrothermal upgrading process configured to utilize supercritical water to produce stable hydrocarbon products from a wide range of mixed plastic waste in a hydro processing unit.
In examples, the process may reduce the formation of diolefins or elimination of separate Diolefins Saturation Reactor for treating hydrocarbon effluent from hydrothermal liquification into a liquid fuel.
In examples, provided is a method for treating hydrocarbon effluent from hydrothermal liquification into a liquid fuel by removing impurities from a feed slurry contains Plastic Oil, Pyrolysis oil, synthetic oil or distillate from plastic recycle process using a heating medium, through pre-treatment section. Impurities i.e. silicon, chlorides, metals, heteroatoms, etc., are removed in a pre-treatment zone and purified slurry may be allowed to pass into feed drum or a continuous mixed settler vessel. An internal skewed blade type mixed with blades or any agitator may be used in the continuous mixed settler vessel to establish a stable suspension. The product recycle stream from the bottom of a stripper or a fractionator may be sent to the continuous mixed settler vessel which helps to create an intensive mixing in the bottom of the vessel to disperse settling of any fine solid particles present in the feed. The continuous stirred mixed vessel helps to eliminate any agglomeration of gums that can be formed over time because of the nature of the feedstock. Due to the varied nature of the feedstock, the feed can have occasional peaks of higher diene content (though for a small period) which has tendency to form more gumming material and hence the continuous mixed settler vessel helps to eliminate any agglomeration of gums. The added advantage of bringing in product recycle to the mixed settler vessel enables significant dilution of the feedstock.
In some examples, the continuous mixed settler vessel may be a vertical vessel having a conical bottom which may enable easy removal of any fine solid particles over time.
In some examples, a separate diolefins saturator may be provided downstream of the continuous mixed settler vessel if the feed dienes are expected to be high. The feed is introduced into atleast one Hydro-processing reactor (any reactor with hydrogen presence for reaction—this can be olefinic saturation (whether linear, di or cyclic olefins, treating of heteroatoms like sulfur, nitrogen, oxygen or any halides such as chlorides, fluorides, bromides or any shift in the boiling point of the feed due of the cracking of the molecules—more specifically referred as hydrocracking) with hydrogen at a temperature between 180 and 500° C., and a hydrogen partial pressure between 20.0 to 180.0 barg to obtain a hydrogenated effluent. The reactor effluent is passed to a separator consisting of hot high pressure and a cold high pressure separator. The reactor effluent is mixed with make-up or recycled hydrogen in hot high pressure separator at a temperature 180 to 380° C., and a hydrogen partial pressure between 15.0 to 170.0 barg. The overhead stream of the hot high pressure separator is mixed with water to dissolve chlorides/salts, which is then removed as sour water. Finally, the separator effluent is passed to a distillation section for extracting a liquid fuel product stream. A portion of the hydro treated product stream may be recycled to the continuous mixed settler vessel, which reduces the concentration of diolefins.
So that the recited features of the present invention can be understood in detail, a more particular description of the invention may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
Hydrothermal liquefaction (HTL) process is a method used to convert plastic waste in the presence of supercritical water into plastic oils. The cold plastic oil feed at 0-12 barg and 20-100° C. is received at the battery limit.
It should be noted that, to process these feeds, high-severity operating conditions (e.g., more severe operating conditions, such as higher temperatures and pressure) are generally involved to produce products having a higher value than the feed. High-severity operating conditions enable methane cracking and aromatic ring cracking, which do not occur at appreciable rates at typical low-severity conditions (e.g., conventional steam cracking conditions). High-severity and low-severity conversion processes are typically based on different pyrolysis reactors, which may include pyrolysis alone or integrated with combustion chemistry. That is, the reactors may include pyrolysis chemistry (e.g., thermochemical decomposition of feed at elevated temperatures in the absence of oxygen) alone or in combination with combustion chemistry (i.e., exothermic chemical reactions between a feed and an oxidant). These pyrolysis reactors can be divided into different types: partial combustion that burns part of the pyrolysis feed, indirect combustion that involves contacting the pyrolysis feed with combustion products, are process that generate the electric arc or plasma to crack the pyrolysis feed, and thermal pyrolysis. Each of these pyrolysis types differs in the means of generating and transferring the heat for the pyrolysis, but can be broadly characterized as low-severity or high-severity.
The term “high-severity” means pyrolysis conditions resulting in the conversion of the pyrolysis feed comprising hydrocarbons to make a product based on the weight of the hydrocarbons in the pyrolysis feed. The operating conditions for a thermal pyrolysis reactor may be characterized by a severity threshold temperature that divides low-severity operating conditions in thermal pyrolysis reactors from high-severity operating conditions in thermal pyrolysis reactors. The high-severity operating conditions for a thermal pyrolysis reactor may be characterized as peak pyrolysis gas temperatures that are greater than the severity threshold temperature. The low-severity thermal pyrolysis reactor may be characterized as pyrolysis gas temperatures that are less than the severity threshold temperature and no pyrolysis gas temperatures that exceed the severity threshold temperature.
The HP Feed Pump takes suction from the Feed Surge Drum (V01) and pumps the feed to the required reactor pressure. The oil flow rate is controlled with a flow control valve immediately downstream of the Feed Pump (P01). The pumped feed is then mixed with hydrogen-rich treat gas and preheated against reactor effluent where it is heated to the required reactor inlet temperature by a temperature controller resetting duty. Treat gas is injected upstream of Feed/Effluent Exchanger as the feed contains cracked feedstock which tends to polymerize. The presence of H2 inhibits polymerization thereby reducing the fouling tendency in the Feed/Effluent Exchanger.
The Guard Reactor system consists of single or multiple reactors with one to many fixed beds to process the plastics oil along with the stripped or fractionated bottoms recycle stream. The primary conversion gas products from the reactors are routed through the trickle bed reactor in downward flow. The pressure level for this reaction is approximately between 20-180 barg with temperatures ranging from 180° C. to 500 C.
The contaminants from the plastics oil are first removed and then hydrotreated or cracked to achieve product specifications. The optimum inlet temperature of the reactor depends on the space velocity and catalyst activity; therefore, it depends on the age of reactor catalyst (Start-of-run, SOR/End-of-run, EOR).
The operating pressure of reactor is mainly dependent upon HDN (Hydrodenitrogenation) or HDO (Hydrodeoxygenation). Typically, the feeds containing nitrogen in the form of carbazoles or acridines are more difficult to crack than nitriles. Similarly, phenols are stable and resistant to hydrotreating so if a large fraction of the oxygen is in phenols, then higher pressure is recommended. Chlorides in the form of PCBs (Polychlorinated biphenyls) is highly reactive and converts to HCl easily. The conversion of these species starts around 250° C.
A small purge stream of Make-up or fresh hydrogen (190) is used to strip off chlorides or HCl entrained in the HHPS Liquid. Most of the HCl will remain in the vapor phase and will be water washed in the overhead circuit. There will be some residual HCl saturated in the HHPS liquid.
Wash water (203) is injected continuously upstream of the Reactor Effluent Air Cooler (AC01) to dissolve NH3 and H2S in the reactor effluent, thereby preventing exchanger tube plugging due to the deposition of ammonium salts. The reactor effluent is cooled in the Reactor Effluent Air Cooler to <70° C. This air cooler increases the purity of the gas leaving the Cold High Pressure System CHPS (V03) and ensures sufficient quench gas temperature at Recycle Gas Compressor outlet.
The cooled reactor effluent is then sent to the Cold High-Pressure Separator (V03) where the vapor, liquid, and water phases are separated. The sour water (206) from the Cold High-Pressure Separator is sent to the battery limit on interface level control. The hydrocarbon liquid from the Cold High-Pressure Separator is withdrawn on level control and is routed directly to the Product Stripper overhead drum. The CHPS liquid (137) combines with the stripper overhead condenser outlet stream before it goes to stripper overhead drum (142).
The product (162) recycling from the bottoms of the stripper or fractionator (169) to surge/continuous mixed settler vessel (V01) which eliminates the need for a diolefin reactor, reduces the concentration of diolefins, control the differential temperature (dT) which helps to control temperature rise due to olefinic saturation in the first bed and significantly reduces recycle gas quench to save on compression costs.
Hydrothermal liquefaction (HTL) process is a method used to convert plastic waste in the presence of supercritical water into plastic oils. The cold plastic oil feed at 0-12 barg and 20-100° C. is received at the battery limit. This cold feed (100) is sent to Feed Coalescer (V02) to remove free water and water-soluble impurities and routed to Feed Contaminant Removal System (V02) to remove contaminants such (mercury, arsenic, sodium, potassium, etc) at lower severity. This system (V02) uses filters or an adsorbent bed to remove the impurities. The impurities removed plastic oil feed (102) is filtered in the Feed Filter (F01) to avoid carryover of catalyst fines to prevent plugging and pressure buildup in the downstream High Pressure (HP) reactors.
Optionally, the feed (102) may be heated and may be sent to a continuous mixed settler vessel (V01). An internal skewed blade type mixed with blades or any agitator may be required in the continuous mixed settler vessel (V01) to establish a stable suspension. The product recycle stream from the bottom of the Stripper or Fractionator may be sent to the continuous mixed settler vessel (V01) helps to create an intensive mixing in the bottom of the vessel to help disperse settling of any fine solid particles present in the feed (102). The continuous stirred mixed vessel (V01) helps to eliminate any agglomeration of gums that can be formed over time because of the nature of the feedstock. Due to the varied nature of the feedstock, the feed (102) may have occasional peaks of higher diene content (though for a small period) which has tendency to form more gumming material and hence the continuous mixed settler vessel helps with this concern. The added advantage of bringing in product recycle to this drum enables significant dilution of the feedstock.
The continuous mixed settler vessel (V01) may be a vertical vessel with can also have a conical bottom to enable easy removal of any fine solid particles over time.
In some examples, a separate diolefins saturator may also be provided downstream of this continuous mixed settler vessel (V01) if the feed dienes are expected to be high.
The HP Feed Pump (P01) may take suction from the continuous mixed settler vessel (V01) and pumps the feed (102) to the required reactor pressure. The oil flow rate is controlled with a flow control valve immediately downstream of the Feed Pump (P01). The pumped feed is then mixed with hydrogen-rich treat gas and preheated against reactor effluent where it is heated to the required reactor inlet temperature by a temperature controller resetting duty. Treat gas is injected upstream of Feed/Effluent Exchanger as the feed contains cracked feedstock which tends to polymerize. The presence of H2 inhibits polymerization thereby reducing the fouling tendency in the Feed/Effluent Exchanger.
The hydroprocessing reactor consists of Guard Bed Reactor (taking care of contaminants such as silicon, arsenic, lead, phosphorus, nickel, vanadium, calcium, iron, tin, lead, antimony, and other metals, halogens such as chlorides, fluorides, bromides), Hydrotreating Reactor (taking care of heteroatoms such as Sulfur, Nitrogen, Oxygen) and Hydrocracking Reactor (taking care of aromatic saturation and boiling point shift) are the main components that will be utilized to achieve the desired process objectives. The reactions involved are exothermic, causing a temperature rise across each catalyst bed.
The Guard Reactor system consists of single or multiple reactors with one to many fixed beds to process the plastics oil along with the stripped or fractionated bottoms recycle stream. The primary conversion gas products from the reactors are routed through the trickle bed reactor in downward flow. The pressure level for this reaction is approximately between 20-180 barg with temperatures ranging from 180° C. to 500 C.
The contaminants from the plastics oil are first removed and then hydrotreated or cracked to achieve product specifications. The optimum inlet temperature of the reactor depends on the space velocity and catalyst activity; therefore, it depends on the age of reactor catalyst (Start-of-run, SOR/End-of-run, EOR).
The operating pressure of reactor is mainly dependent upon HDN (Hydrodenitrogenation) or HDO (Hydrodeoxygenation). Typically, the feeds containing nitrogen in the form of carbazoles or acridines are more difficult to crack than nitriles. Similarly, phenols are stable and resistant to hydrotreating so if a large fraction of the oxygen is in phenols, then higher pressure is recommended. Chlorides in the form of PCBs (Polychlorinated biphenyls) is highly reactive and converts to HCl easily. The conversion of these species starts around 250° C.
The cooled reactor effluent flows to a Hot High-Pressure Separator for vapor-liquid separation. The feed bypass control valve across the Feed/Effluent Exchanger ensures that the desired HHPS temperature of around 180-380° C. is met. The pressure of the Hot High Pressure separator can range from 15 barg to 170 barg depending upon the severity of the system. The design ensures Hot High Pressure Separator temperature is maintained sufficiently above the calculated deposition temperature (180-380° C.) based on the chloride level specified in the design basis. The HHPS liquid from the Hot High-Pressure Separator is let down and sent to Stripper on level control.
A small purge stream of Make-up or fresh hydrogen is used to strip off chlorides or HCl entrained in the HHPS Liquid. Most of the HCl will remain in the vapor phase and will be water washed in the overhead circuit. There will be some residual HCl saturated in the HHPS liquid.
Wash water is injected continuously upstream of the Reactor Effluent Air Cooler to dissolve NH3 and H2S in the reactor effluent, thereby preventing exchanger tube plugging due to the deposition of ammonium salts. The reactor effluent is cooled in the Reactor Effluent Air Cooler to <70° C. This air cooler increases the purity of the gas leaving the CHPS and ensures sufficient quench gas temperature at Recycle Gas Compressor outlet.
The cooled reactor effluent is then sent to the Cold High-Pressure Separator where the vapor, liquid, and water phases are separated. The sour water from the Cold High-Pressure Separator is sent to the battery limit on interface level control. The hydrocarbon liquid from the Cold High-Pressure Separator is withdrawn on level control and is routed directly to the Product Stripper overhead drum. The CHPS liquid combines with the stripper overhead condenser outlet stream before it goes to stripper overhead drum. Vapor from the Cold High-Pressure Separator is sent to Recycle Gas Compressor Knockout Drum for use as recycled gas. Due to the low amount of sulfur in the feed, no amine scrubbing is required.
The Product Stripper or Fractionator is a steam-stripped column designed to remove light ends, including H2S and NH3, from the HHPS liquid effluent stream that is fed to the column. Stripping of the butanes and lighter components overhead is accomplished using LP-HP stripping steam. Liquid from the Hot High-Pressure Separators is fed to the Product Stripper. There may or may be not any requirement of external heat source to this column; the heat necessary for the column may be supplied by the preheated feed or an external heater depending on the product specifications.
The product recycling from the bottoms of the stripper or fractionator to the continuous mixed settler vessel which eliminates the need for a diolefin reactor in some examples when the feed diene content is low but in general is more advantageous due to the significant dilution, reduces the concentration of diolefins, control the differential temperature (dT) which helps to control temperature rise due to olefinic saturation in the first bed and significantly reduces recycle gas quench to save on compression costs.
In some examples, the diameter of the reactor can be increased at minimum mass flux which helps maintain the minimum reactor mass flux, which allows for a more reasonable reactor L/D.
In some examples, a hydrothermal liquefaction process and system are described. In examples, the hydrothermal liquefaction process may be used to convert waste plastic feedstock. In examples, the hydrothermal liquefaction process as described may include the presence of supercritical water acting as heating medium. In examples, the products derived from the described process and system may be more stable and/or provide high quality plastic oils with low solids, water, and impurities content. In examples, the process and system as described may allow a much simpler hydro treatment process of the plastic oils into steam cracker feedstock or clean liquid fuel products.
In some examples, the hydrothermal liquefaction process and system as described may employ the use of supercritical water as a heating medium. In examples, the supercritical water may be mixed with the plastic waste in the reactor. In examples, this may provide a more efficient and more homogeneous (i.e., with no temperature gradient) heat transfer compared to other advanced recycling processes (e.g., pyrolysis), where plastic waste is heated by the reactor itself.
In examples, the plastic oil derived from the described HTL process may include a negligible amount of char. In examples, the produced plastic oil may be fed to a hydro treatment process unit tailored to produce market tradable products.
In examples, hydro treatment process as described may include selective removal of impurities at low severity.
The cold feed at 0-12 barg and 20-100° C. is received at the battery limit. This cold feed is sent to Feed Coalescer to remove free water and water-soluble impurities and routed to Feed Contaminant Removal System to remove contaminants such (mercury, arsenic, sodium, potassium, etc) at lower severity.
Mercury is most likely to be present as elemental mercury. It also be present as organo-metallic and ionic mercury. Organo-mercury compounds are easily broken down into elemental mercury when heated in a reducing atmosphere, so much of it is expected to be elemental mercury in the C3 to C6 product streams. The main concerns are corrosion, poisoning of catalysts, and safety issues. It is therefore critical to remove elemental mercury to less than 1 ppbw in the products. Arsenic in the form of Arsine (AsH3) can be easily removed at lower temperatures. This can be coupled with the Mercury removal system. Whereas organic arsenic compounds will need high temperatures for removal. Similarly, this low severity system can be used to remove sodium and potassium salts in the feed. This solution enables metals like arsine, mercury, sodium, potassium, etc. to be removed from the system that will enable an optimum balance between cold and hot system guard bed catalysts. This system can use filters or an adsorbent bed system to remove the impurities. This feed is filtered in the Feed Filter to avoid carryover of catalyst fines to prevent plugging and pressure buildup in the downstream High Pressure (HP) reactors.
In examples, the hydro treatment process may include dilution of feed with product to reduce the feed dienes content which can result in elimination of separate low severity hydrogenation reactor.
Most refiners use separate di-olefins reactor to saturate dienes in the waste plastics oil. Waste plastics oil is associated with high diene content in the feed and as result it polymerizes at elevated temperatures. A dedicated diolefins saturation reactor is required at temperature operating at no more than 210° C. to ensure that these highly reactive species are removed from the feed before polymerization can take place.
The plastics oil from the hydrothermal liquefaction processes are generally accompanied by low diene value. The bottoms product from the stripper or fractionator in the process may be recycled back to the continuous mixed settler vessel to mix with the fresh feed. As a result, the final concentration of the most reactive dienes will be low and will not cause pressure drop (dP) issues.
The requirement of a separate DIOS Reactor is more of a risk assessment with the risk of the unit developing pressure drop issues within the target cycle length increasing with increasing feed diene. The specification of feed diene<1.2 will be even further lower due to dilution with the product recycle. As a result, the final concentration of the most reactive dienes will be low enough not to cause dP issues in the short cycle length that the unit can run due to contaminants. But occasional feed diene excursions or levels up to 3.0 in the feed could make the risk of dP issues higher. In this case (if higher levels are expected) adding the DIOS rector may increase reliability.
If the diene concentration is expected to be <1.2 most of the time and turnaround time is 1 year for the guard reactor catalysts, it is generally recommended for no separate DIOS reactor. However, the DIOS reactor can be added if there are reliably concerns.
The DIOS reactor is generally operated at a temperature of less than 200° C. The temperature of the reactor is adjusted to allow a very small reactor exotherm (up to 5° C.). This is to remove the most reactive dienes in the feed. The olefinic saturation starts at around 250° C. and will lead to very high exotherms. So, there is a very narrow temperature window between 200-250° C. for safe operation of the DIOS reactor.
The product recycling from the bottoms of the stripper or fractionator to surge or continuous mixed settler vessel serves 3 purposes: Eliminate the need for a DIOS reactor-helps to dilute the feed diene, Control differential temperature (dT)—helps to control temperature rise due to olefinic saturation in the first bed. Significantly reduces recycle gas quench to save on compression costs, Increase the reactor diameter at minimum mass flux—helps maintain the minimum reactor mass flux, which allows for a more reasonable reactor L/D.
In examples, the hydro treatment process may include involve using a hydro treatment processing reactor in the presence of hydrogen to obtain effluent.
The HP Feed Pump may take suction from the continuous mixed settler vessel and pumps the feed to the required reactor pressure. The oil flow rate is controlled with a flow control valve immediately downstream of the Feed Pump. The pumped feed is then mixed with hydrogen-rich treat gas and preheated against reactor effluent in the Feed/Effluent Exchanger. Treat gas is injected upstream of Feed/Effluent Exchanger as the feed contains cracked feedstock which tends to polymerize. The presence of H2 inhibits polymerization thereby reducing the fouling tendency in the Feed/Effluent Exchanger. The gas-to-oil ratio is an important factor in ensuring complete reaction in the reactor. As a result, the gas to oil ratio is closely monitored. In case the gas to oil ratio falls below the minimum value, the oil feed to the units needs to be reduced to maintain the gas to oil ratio.
The combined feed is heated in the Feed/Effluent Exchanger and then routed to Reactor Feed Heater, where it is heated to the required reactor inlet temperature by a temperature controller resetting duty.
Immediately upstream of the reactor, a final temperature control is used to perform any fine tuning on the reactor inlet stream temperature. If there is a need for a cooler reactor inlet temperature, quench hydrogen will be added via a temperature controller resetting quench flow control.
The hydroprocessing reactor can consist of Guard Bed Reactor (taking care of contaminants such as silicon, arsenic, lead, phosphorus, nickel, vanadium, calcium, iron, tin, lead, antimony, and other metals, halogens such as chlorides, fluorides, bromides), Hydrotreating Reactor (taking care of heteroatoms such as Sulfur, Nitrogen, Oxygen) and Hydrocracking Reactor (taking care of aromatic saturation and boiling point shift) are the main components that will be utilized to achieve the desired process objectives. The reactions involved are exothermic, causing a temperature rise across each catalyst bed.
The Guard Reactor system can consist of single or multiple reactors with one to many fixed beds to process the plastics oil along with the stripped or fractionated bottoms recycle stream. The primary conversion gas products from the reactors are routed through the trickle bed reactor in downward flow. The pressure level for this reaction is approximately between 20-180 barg with temperatures ranging from 180° C. to 500 C.
The contaminants from the plastics oil are first removed and then it can be hydrotreated or cracked to achieve product specifications. The optimum inlet temperature of the reactor depends on the space velocity and catalyst activity; therefore, it depends on the age of reactor catalyst (Start-of-run, SOR/End-of-run, EOR).
The first bed will have a guard bed which serves to trap the particles in the case of a fouling service as well as the solids and micro-particulates (and/or metals) in the plastics oil. The reactions involved are exothermic, causing a temperature rise across each catalyst bed. The recycle from stripper or fractionator bottoms act as quench to control the heat rise due to the saturation of the olefins. Cold recycle gas from the Recycle Gas Compressor can also be injected, on temperature control, as quench between catalyst beds to control the average catalyst temperatures and to limit bed outlet temperatures. The weighted average bed temperatures determine the extent of hydrotreating and hydrocracking reactions. The catalyst beds are separated by inter-bed quench and distribution systems, which provide state of the art feed distribution and temperature control. For highly exothermic reaction systems, uniform temperature distribution across the reactor is extremely critical to avoid hot spots that can lead to unsafe conditions. The benefits of the inter-bed quench and distribution systems include reactor temperature control, maximum catalyst utilization and the highest degree of safety and reliability. Catalyst performance is determined by a combination of operating conditions (temperature, hydrogen partial pressure, and charge rate and gas-to-oil ratio) imposed on the GPH reactor system.
The operating pressure of this unit is mainly dependent upon HDN (Hydrodenitrogenation) or HDO (Hydrodeoxygenation). Typically, the feeds containing nitrogen in the form of carbazoles or acridines are more difficult to crack than nitriles. Similarly, phenols are stable and resistant to hydrotreating so if a large fraction of the oxygen is in phenols, then higher pressure is recommended. Chlorides in the form of PCBs (Polychlorinated biphenyls) is highly reactive and converts to HCl easily. The conversion of these species starts around 250° C.
In examples, the hydro treatment process may include separation of the effluent into product fractions.
The heat content of reactor effluent is recovered in Feed/Effluent Exchanger. The cooled reactor effluent flows to a Hot High-Pressure Separator for vapor-liquid separation. The feed bypass control valve across the Feed/Effluent Exchanger ensures that the desired HHPS temperature of around 180-380° C. is met. The pressure of the Hot High Pressure separator can range from 15 barg to 170 barg depending upon the severity of the system. The design ensures Hot High Pressure Separator temperature is maintained sufficiently above the calculated deposition temperature (180-380° C.) based on the chloride level specified in the design basis. The HHPS liquid from the Hot High-Pressure Separator is let down and sent to Stripper on level control.
A small purge stream of Make-up hydrogen is used to strip any HCl entrained in the HHPS Liquid. Most of the HCl will remain in the vapor phase and will be water washed in the overhead circuit. There will be some residual HCl saturated in the HHPS liquid. Since we are dealing with a high concentration of HCl in the reactor effluent, it is necessary to ensure the concentration of HCl is minimized as low as possible.
The target is to achieve a very low concentration of HCl in the HHPS liquid to ensure the operating temperature of the downstream Product Stripper overhead is always above the deposition temperature at those conditions.
Wash water is injected continuously upstream of the Reactor Effluent Air Cooler to dissolve NH3 and H2S in the reactor effluent, thereby preventing exchanger tube plugging due to the deposition of ammonium salts. The reactor effluent is cooled in the Reactor Effluent Air Cooler to <70° C. This air cooler increases the purity of the gas leaving the CHPS and ensures sufficient quench gas temperature at Recycle Gas Compressor outlet.
The cooled reactor effluent is then sent to the Cold High-Pressure Separator where the vapor, liquid, and water phases are separated. The sour water from the Cold High-Pressure Separator is sent to the battery limit on interface level control. The hydrocarbon liquid from the Cold High-Pressure Separator is withdrawn on level control and is routed directly to the Product Stripper overhead drum. The CHPS liquid combines with the stripper overhead condenser outlet stream before it goes to stripper overhead drum. Vapor from the Cold High-Pressure Separator is sent to Recycle Gas Compressor Knockout Drum for use as recycled gas. Due to the low amount of sulfur in the feed, no amine scrubbing is required.
The Product Stripper or Fractionator is a steam-stripped column designed to remove light ends, including H2S and NH3, from the HHPS liquid effluent stream that is fed to the column.
Stripping of the butanes and lighter components overhead is accomplished using LP-MP stripping steam. Liquid from the Hot High-Pressure Separators is fed to the Product Stripper. There may or may be not any requirement of external heat source to this column; the heat necessary for the column can be supplied by the preheated feed or an external heater depending on the product specifications.
A method for treating a hydrocarbon effluent from hydrothermal liquification into a liquid fuel by removing impurities from a feed slurry contains Plastic Oil, Pyrolysis oil, synthetic oil or distillate from plastic recycle process using a heating medium, through pre-treatment section. Impurities i.e. silicon, chlorides, metals, heteroatoms, etc., are removed in a pre-treatment zone and purified slurry may be passed into a continuous mixed settler vessel. The feed is introduced into atleast one Hydro-processing reactor with hydrogen at a temperature between 180 and 500° C., and a hydrogen partial pressure between 20.0 to 180.0 barg to obtain a hydrogenated effluent. The reactor effluent is passed to a separator consists of hot high pressure and a cold high pressure separators. The reactor effluent is mixed with make-up or recycled hydrogen in hot high pressure separator at a temperature 180 to 380° C., and a hydrogen partial pressure between 15.0 to 170.0 barg. The overhead stream of the hot high pressure separator is mixed with water to dissolve chlorides/salts, which is then removed as sour water. Finally, the separator effluent is passed to a distillation section for extracting a clean liquid fuel product stream.
In examples, a preheated feed is mixed with a portion of the hydrotreated product that is recycled back through the reactor system to dilute diene in the feed. As a result, the final concentration of the most reactive dienes will be low enough not to cause pressure drop (dP) issues in the short cycle length.
A method for treating a hydrocarbon effluent from hydrothermal liquification of plastic waste into a liquid transportation fuel by removing impurities from a feed slurry contains Plastic Oil, Pyrolysis oil, synthetic oil or distillate from plastic recycle process using a heating medium, through pre-treatment section. Impurities i.e. silicon, chlorides, metals, heteroatoms, etc., are removed in a pre-treatment zone and purified slurry may be passed into a feed drum or a continuous mixed settler vessel. The feed is introduced into a Hydro-processing reactor with hydrogen at a temperature between 18° and 500° C., and a hydrogen partial pressure between 20.0 to 180.0 barg to obtain a hydrogenated effluent. The reactor effluent is passed to a separator consists of hot high pressure and a cold high pressure separators. The reactor effluent is mixed with make-up or recycled hydrogen in hot high pressure separator at a temperature 180 to 380° C., and a hydrogen partial pressure between 15.0 to 170.0 barg. The overhead stream of the hot high pressure separator is mixed with water to dissolve chlorides/salts, which is then removed as sour water. Finally, the separator effluent is passed to a distillation section for extracting a liquid fuel product stream. A portion of the hydro treated product stream may be recycled to the continuous mixed settler vessel, which reduces the concentration of diolefins.
In examples, the hydro treatment process as described may produce a higher quality liquid fuel product than other plastic oil-to-fuel processes, such as pyrolysis, because the process can operate at higher pressures and temperatures.
The Table 1 below presents typical product specifications achieved in the process depending upon the level of hydrogen severity. A lower severity system will target contaminant removal (metals such as silicon, arsenic, mercury, halogens (such as Chloride, Fluoride, Bromide), etc.), olefin saturation (olefins saturated to paraffins) and heteroatom removal (Sulfur, Nitrogen, Oxygen). Whereas a higher severity system will additionally target aromatic saturation (Aromatics such mono, di, tri (poly) saturated to alkanes), and boiling point shift (higher boiling fractions shift to lower boiling point) as depicted in Table 2.
An advantage in the hydro treatment process described herein may be that the hydro treated product recycle can reduce diolefin content in the feed and eliminates the requirement of separate di-olefins reactor. In examples, this may lead to capital investment savings in the design of the waste plastics oil upgrader unit.
Another advantage of the hydrotreatment process described herein may be that the plastic oil upgrading may be limited by the cycle length of the catalyst to trap very high conversion elevated contaminant levels.
A Typical plastics oil from processes other than hydrothermal liquefaction will have very high levels of contaminants. Please see table 3 below.
The catalyst volume required to remove these contaminant levels will be very high which necessitates large reactor diameters. The reactor diameters are set by the mass flux (mass per area) to keep with the optimized design performance of the process. This in turn sets the limit on the volume of the catalyst hence life of the catalyst.
In examples, the plastics oil upgraded from the above described HTL process may needs less catalyst volume to trap impurities. In examples, this may result in higher cycle length, a lower capital cost, and lower operating cost.
For example, a typical pyrolysis oil with Silicon level at 200 ppm, the catalyst would last only 2.5 months compared to a silicon level of 20 ppm that would give more than 2 years on the catalyst life.
A frequent change-out of the catalyst will be associated with unit downtime, loss of production, increased catalyst unloading (spent catalysts are generally not regenerable due to high metals loading)/loading (new catalyst loading, catalyst activation) costs.
These directly contribute to a higher capital and operation cost for the typical pyrolysis oil system.
Certain embodiments and features have been described using a set of numerical upper limits and a set of numerical lower limits. It should be appreciated that ranges from any lower limit to any upper limit are contemplated unless otherwise indicated. Certain lower limits, upper limits and ranges appear in one or more claims below. All numerical values are “about” or “approximately” the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art.
Various terms have been defined above. To the extent a term used in a claim is not defined above, it should be given the broadest definition persons in the pertinent art have given that term as reflected in at least one printed publication or issued patent. Furthermore, all patents, test procedures, and other documents cited in this application are fully incorporated by reference to the extent such disclosure is not inconsistent with this application and for all jurisdictions in which such incorporation is permitted.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
This application claims priority to U.S. Provisional Patent Application having Ser. No. 63/588,111 filed on Oct. 5, 2023 which is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 63588111 | Oct 2023 | US |
