Abstract: An improved fluid catalytic cracking process providing improved product yield and selectivity which employs a split flow of recycled, regenerated catalyst to the reactor riser. Process operating temperatures control the flow rates of the recycled, regeneration catalyst.

Abstract: In a selective hydrogenation process wherein at least two catalyst beds in series are utilized, the temperature of the feed stream to the first catalyst bed and the temperature of the feed stream from the first catalyst bed to the second catalyst bed is controlled so as to maintain a desired reaction temperature in both catalyst beds and to maintain a desired relationship between the amount of the impurity selectively hydrogenated in the first catalyst bed and the amount of the impurity selectively hydrogenated in the second catalyst bed.

Abstract: A fractionation column is provided with a feed inlet and three product outlets, with the product outlets including an overhead vapor outlet, a bottoms liquid outlet and a side draw outlet. A plurality of vertically spaced apart vapor-liquid contact trays are mounted in the column. A generally vertical partition is positioned within the column in a central region between an upper and a lower vapor-liquid contact tray and divides the central region into first and second chambers defined by the upper and lower trays, column shell and partition. The feed inlet opens into the first chamber while the side draw outlet opens into the second chamber. First control means is provided for controlling the various inputs and outputs of the column. Second control means is also provided for measuring various constituent portions of fluid mixtures within the column.

Abstract: A system for regulating and optimizing process conditions, such as octane number, aniline point or density of reformed hydrocarbons, by manipulating various process variables in order to control the process, both in accordance with a regulatory effect, namely, such as to cause the process to achieve and maintain the desired setpoint and setpoints for the process condition or conditions, and in accordance with an optimizing effect, namely, such as to cause the process to achieve some predetermined state defined as optimum. The effects are not necessarily consistent, but relative weights are assigned to the two effects such that the regulating effect is paramount until the process condition or conditions are substantially at setpoint or setpoints, at which time the regulating effect is minimum, thus allowing the optimizing effect to influence the process.

Abstract: In the purification of hydrocarbon streams containing HF by chemical reaction with potassium hydroxide, a small portion of the hydrocarbon stream containing HF is passed through a small test bed of solid KOH; and when excess HF is present in the hydrocarbon stream to be purified, the temperature of the test bed increase significantly and rapidly and the flow of hydrocarbon is discontinued to the main treater responsive to the temperature in the test bed thereby preventing the treater temperature from exceeding a preselected maximum allowable value. In one embodiment, the main hydrocarbon charge is by-passed around the main KOH treater and introduced into the effluent from the treater; and in another embodiment, the hydrocarbon charge is returned to a settling zone following alkylation and prior to separation facilities utilized to process the hydrocarbon phase.

Abstract: A refining unit treats heavy sour charge oil with N-methyl-2-pyrrolidone solvent, hereafter referred to as MP, in a refining extractor to yield raffinate and extract mix. The MP is recovered from the raffinate and from the extract mix and returned to the refining extractor. A system controlling the refining unit includes a gravity analyzer, a sulfur analyzer and viscosity analyzers; all analyzing the heavy sour charge oil and providing corresponding signals, a refractometer samples the charge oil and provides a signal corresponding to the RI, sensors sense the flow rates of the charge oil and the MP flowing into the refining tower and the temperature of the extract mix and provide corresponding signals. One of the flow rates of the heavy sour charge oil and the MP flow rates is controlled in accordance with the signals from all the analyzers, the refractometer and all the sensors, while the other flow rate of the heavy sour charge oil and the MP flow rates is constant.

Abstract: A refining unit treats heavy sweet charge oil with a methyl-2-pyrrolidone solvent, hereafter referred to as MP, in a refining tower to yield raffinate and extract mix. The MP is recovered from the raffinate and from the extract mix and returned to the refining tower. A system controlling the refining unit includes a gravity analyzer, a refractometer, a sulfur analyzer and viscosity analyzers; all sampling the heavy sweet charge oil and providing corresponding signals. Sensors sense the flow rates of the charge oil and the MP flowing into the refining tower and the temperature of the extract mix and provide corresponding signals. One of the flow rates of the heavy sweet charge oil and the MP flow rates is controlled in accordance with the signals from all the analyzers, the refractometer and all the sensors, while the other flow rate of the heavy sweet charge oil and the MP flow rates is constant.

Abstract: Apparatus for regenerating at elevated temperature a fluidized mass of particles, e.g., a catalyst used in treatment of hydrocarbons, e.g., fluidized catalysts cracking of oil, is disclosed.Several operations can be effected in the apparatus, each of them alone or in various combinations.An operation basic to the overall operation, always effected by the apparatus, is the continuous circulation of dense phase particles undergoing regeneration from a dense phase or fluidized regeneration vessel to a hot surge vessel and from the latter back into the dense phase bed in the regeneration vessel.Used catalyst can be in part passed to the hot surge vessel whenever it is tending to cause undue temperature rise in the regeneration vessel.Fresh or unused catalyst can be fed to the regeneration vessel continuously or intermittently responsive to sensed temperature change in said vessel and/or to said hot surge vessel.

Abstract: In a reactor for cracking heavy hydrocarbon oil through a fluidized bed of particles of natural ores, coke-like materials are deposited on a top of the reactor or pipe inside surfaces of a transfer line from the reactor to a scrubber. To effectively scour out the deposited coke-like materials, particles of natural ores having a mean diameter of a few hundred .mu.m is made to be contained in an effluent gas from the top of reactor, passing through the transfer line at a concentration of 1 to 40 g/m.sup.3. The particles of natural ores have a good effect of scouring out the deposited coke-like materials and can keep the transfer line efficiently clean even with a small amount of the particles of natural ores, decreasing a pressure drop in the transfer line.

Abstract: The flow of air into a catalyst regenerator is automatically controlled by controlling a side air stream responsive to a computed desired total air flow signal and by controlling a main air stream at a constant value. This constant value is changed if two conditions simultaneously occur: The time elapsed since the last change of said constant value is not shorter than a given minimal value, and the control of the side air stream exceeds the limit of the side air controller.

Abstract: Coronene deposits are removed from a heat exchange zone disposed in two parallel trains of heat exchangers in a reforming process by reducing the flow of reforming zone effluent in one of the trains of heat exchangers sufficiently to effect condensation of a portion of the reforming zone effluent in said one train of heat exchangers where the coronene is deposited while simultaneously increasing the flow of reforming zone effluent in the second train of heat exchangers. Control means are provided in each of the heat exchange trains.

Abstract: A furfural refining unit treats heavy sweet charge oil with a furfural solvent in a refining tower to yield raffinate and extract mix. The furfural is recovered from the raffinate and from the extract mix and returned to the refining tower. A system controlling the refining unit includes a gravity analyzer, a flash point temperature analyzer, a sulfur analyzer and viscosity analyzers; all analyzing the heavy sweet charge oil and providing corresponding signals, sensors sense the flow rates of the charge oil and the solvent flowing into the refining tower and the temperature of the extract mix and provide corresponding signals. One of the flow rates of the heavy sweet charge oil and the furfural flow rates is controlled in accordance with the signals from all the analyzers and all the sensors, while the other flow rate of the heavy sweet charge oil and the furfural flow rates is constant.

Abstract: In the fluid catalytic cracking process, improved adaptive behavior of the catalyst section with the regenerator operating in the complete CO-burning mode is achieved by including within the regenerator, as an element of control, variable recycle of regenerated to spent catalyst. In response to excursions of the regenerated catalyst temperature, such as would be caused by change of feedstock, the recycle ratio is altered in a direction to restore the temperature to a predetermined value. The improved control system extends the useful control range, and it also diminishes counterproductive changes in severity induced by disturbances such as change of feedstock quality.

Abstract: In the fluid catalytic cracking process, improved adaptive behavior of the catalyst section with the regenerator operating in the complete CO-burning mode is achieved by including, as elements of control, variable preheat of the oil feed and variable recycle of regenerated catalyst to spent catalyst. In response to excursions of the regenerated catalyst temperature, such as would be caused by change of feedstock, the oil preheat temperature and recycle ratio are altered in a direction to restore the regenerated catalyst temperature to a predetermined value. The improved control system extends the useful control range, and it also diminishes counterproductive changes in severity induced by disturbances such as change of feedstock quality.

Abstract: Coronene deposits are removed from a heat exchange zone of a reforming process by operating the reforming zone at conditions such that at least a portion of the reformer effluent condenses in the heat exchange zone where the coronene deposit occurs.

Abstract: To optimize recovery by the hot water process of hydrocarbons from bituminous sands, an alkaline process aid (e.g. NaOH) is commonly added to the conditioning step. In accordance with this invention, the quantity of process aid added is varied in response to the fines content of the incoming bituminous sands feed.

Abstract: In Fluidized Catalytic Cracking (FCC), the significant advantages of stripper cyclones in the reactor are enhanced by operating the regenerator in CO combustion mode.

Abstract: In a fractionation system wherein a stream of heat-containing fluid is taken from a zone effecting at least a partial control of at least one operating condition in said zone by withdrawing said fluid at a rate responsive to and correlated with a change in said condition and utilizing the heat in said withdrawn fluid.

Abstract: A coking drum system is provided in combination with a process control unit wherein the rate of material delivered to a coking drum during a coking process timing cycle is monitored and the quantity of material received by the coking drum is continuously derived therefrom. Based on this derived quantity of delivered material, the quantity of feed material required to fill the drum to a preestablished level with coke, at the completion of the timing cycle, can be predicted. The flow rate of feed material to the coking drum is accordingly adjusted so that the amount of coke produced in the drum during one timing cycle is optimized.

Abstract: An improved process using a rare earth-containing catalyst is provided. The catalyst comprises a composite of matrix and rare earth or of zeolite, rare earth and matrix, usually alumina. The rare earth can be a single metal or a mixture of rare earth metals. The process involved is the conversion of alcohols or ethers to gasoline boiling range hydrocarbons.

Abstract: The efficiency of a hydrocarbon slurry is maximized by determining the largest percent of economically pumpable distillation overhead that can be obtained from the hydrocarbon. This determination is based on the properties of the overhead as a carrier fluid in the transporting system (e.g. slurry viscosity or pumpability). Once determined, the composition of the optimum overhead is determined by the usual techniques, i.e., by gas chromatographic techniques, to determine its composition and the cut point defined in terms of the composition of the optimum overhead. The composition of the overhead is monitored during the refining process and is compared with the composition of the optimum overhead. The distillation process is then monitored and controlled accordingly to produce an overhead with the desired molecular composition. One advantage of this method is that it limits the amount of undesirable wax crystals in the overhead.

Abstract: By manipulating the degree of stripping of the used or spent catalyst leaving the cracker, the afterburning in a regenerator is controlled both efficiently and rapidly.

Abstract: Control of temperature increase (delta-T) through a reaction zone, in which both exothermic and endothermic reactions are effected, is achieved by sensing the inlet temperature of the charge stock, an intermediate temperature within the reaction zone and the outlet temperature of the effluent from the reaction zone. The inlet temperature sensor co-acts with a temperature recorder controller (TRC) having an adjustable set point, to produce a representative signal which is transmitted to flow-regulating means which adjusts the quantity of charge stock bypassing the feed heater. The difference between the inlet and intermediate temperatures, and that between the intermediate and outlet temperatures are determined to produce two delta-T signals which are transmitted to a double differential temperature recorder controller (DdTRC) which develops a signal representing the difference between the two delta-T signals, compared to a preset difference.

Abstract: Control of temperature increases (delta-T) through a reaction zone, in which both exothermic and endothermic reactions are effected, is achieved by sensing the inlet temperature of the charge stock, a highest temperature from a plurality of intermediate loci within the reaction zone and the outlet temperature of the effluent from the reaction zone. The inlet temperature sensor co-acts with a Temperature Recorder Controller (TRC), having an adjustable set point (control point), to produce a representative signal which is transmitted to flow-regulating means which adjusts the quantity of charge stock bypassing the feed heater. The difference between the inlet and intermediate temperatures, and that between the intermediate and outlet temperatures are determined to produce two delta-T signals which are transmitted to a Double differential Temperature Recorder Controller (DdTRC) which develops a signal representing the difference between the two delta-T signals compared to a preset difference.

Abstract: A cracking reactor is controlled in response to the proportion of heavy aromatic constituents in a feedstock to be cracked.

Abstract: A hydrocarbon stream comprising C.sub.2 to C.sub.8 hydrocarbons is stripped at a high temperature to allow passage of the stripper bottoms stream into a reaction zone without further heating, and the effluent of the reaction zone is then heat exchanged against the feed stream to the stripper column to recover heat. Operation of the reaction zone at the desired temperature is achieved by adjusting the amount of the stripper bottoms stream which is split off for cooling by heat exchange against the feed to the stripper column. The cooled split-off portion is then admixed with the remaining high temperature portion. Adjusting the flow rate of the portion of hot reaction zone effluent which is heat exchanged against the stripper feed stream is performed to control either the temperature of the stripper feed stream or the temperature of the reaction zone effluent as it is passed to a downstream operation.

Abstract: In the removal of HF from hydrocarbon streams by chemical reaction with solid potassium hydroxide, runaway temperatures and subsequent explosions can occur when excess HF is present in the hydrocarbon charged to the KOH treater. According to the invention, a control system and method are provided which regulate the flow of hydrocarbon charged to the KOH treater responsive to temperature changes within the system indicative of excessive amount of HF in the hydrocarbon stream, thereby preventing the treater temperature from exceeding a preselected maximum allowable value. Several embodiments are provided whereby temperature changes in the KOH treater or a differential temperature across an HF stripper are used as temperature sensing points to control flow of hydrocarbon to the KOH treater.

Abstract: A catalytic process for cracking of gas oil is disclosed, wherein trace amounts of metals of Periods 5 and 6 of Group VIII or rhenium is added to the total catalyst inventory so as to enhance significant conversion of the CO in the regenerator while maintaining the efficiency of the cracking reaction at high levels.

Abstract: In the fluid catalytic cracking process, improved adaptive behavior of the catalyst section with the regenerator operating in the complete CO-burning mode is achieved by including, as elements of control, variable preheat of the air feed and variable recycle of regenerated catalyst to spent catalyst. In response to excursions of the regenerated catalyst temperature, such as would be caused by change of feedstock, the air preheat temperature and recycle ratio are altered in a direction to restore the regenerated catalyst temperature to a predetermined value. The improved control system extends the useful control range, and it also diminishes counterproductive changes in severity induced by disturbances such as change of feedstock quality.

Abstract: A fluid catalytic cracking unit is controlled by sensing the reactor bed temperature and the riser temperature and by manipulating the flow of regenerated cracking catalyst into the riser responsive to these two temperature measurements. A gain function generator is utilized to compensate for the non-linear relationship between the change in valve position and change in riser temperature caused thereby.

Abstract: The catalyst circulation rate in a fluid catalytic cracking process is regulated by using a low pressure drop valve means in the spent catalyst circuit of said process in conjunction with a control riser in said circuit. More particularly, a reduced catalyst circulation rate may be obtained in a fluid catalytic cracking process, the spent catalyst circulation rate in said process being controlled by the injection of variable amounts of a control gas into the control riser so as to cause density variations therein, by employing a low pressure drop valve means in the spent catalyst circuit of said process such that the pressure drop across said valve means reduces the pressure drop across the riser and consequently the density within said riser. The reduction in density within the riser results in a lowering of the catalyst circulation rate.

Abstract: In an upflow, ebullated bed reactor using a heterogeneous catalyst, a transport liquid compatible with the catalyst and the reactor feedstock is used. During the addition of fresh catalyst, a heated slurry of catalyst and transport liquid is pumped into the reactor under conditions to minimize (a) the temperature difference between the slurry and the reactor and (b) exposure of the fresh catalyst to a deactivating elevated temperature. During catalyst withdrawal, the temperature of the reactor effluent stream is controlled by mixing with a transport liquid. Measurement and flowability of the resultant mixture is thus assured.

Abstract: A solvent refining unit is controlled so that it has a maximum allowable solvent flow rate or a maximum allowable extract oil flow rate. The temperature of the extract-mix in the refining tower, the flow rate of the charge oil, the flow rate of the solvent and the flow rate of the extract oil are sensed by sensors which provide corresponding signals. A circuit provides signals corresponding to desired flow rates for the charge oil and the solvent and for a desired temperature for the extract-mix in the refining tower. The refining unit is operated in accordance with the desired signals so as to achieve either a maximum allowable flow rate for the solvent or a maximum allowable flow rate for the extract oil, or a maximum allowable flow rate for the refined oil, or a reduced charge oil flow rate for a fixed refined oil flow rate.

Abstract: A hydrocarbon stream comprising benzene is stripped at a high temperature to allow passage of the stripper bottoms stream into a clay treating zone without further heating, and the effluent of the clay treating zone is then exchanged against the feed stream to the stripper column to recover heat. Operation at the optimum clay treating temperature is achieved by adjusting the amount of the stripper bottoms stream which is split off for cooling by heat exchange against the feed to the stripper column. The cooled split-off portion is then admixed with the remaining high temperature portion. Adjusting the flow rate of the portion of hot clay treater effluent which is heat exchanged against the stripper feed stream is performed to control the temperature of either the stripper feed stream or the temperature of the clay treater effluent as it is passed into a downstream fractionator.

Abstract: A method for controlling the production of pitch and the like is disclosed comprising simultaneously measuring the viscosity and temperature of the pitch material from the production unit, comparing the measured value with a predetermined correlation of the viscosity and temperature for the pitch, and adjusting the parameters of the production operation in response to the comparison. An apparatus for carrying out the method is also disclosed comprising a means for withdrawing and returning a sample of the pitch material from the still, a chamber for holding the sample of the pitch material, the chamber having a means for heating and cooling the sample, a temperature sensing device and a viscosity measuring device located in the chamber, and a means for recording the temperature and viscosity values.

Abstract: A method for regulating, or controlling heat input to the reboiler section of a fractionation column. Flow-measuring means, disposed in a substantially liquid-free environment within the confines of the reboiler section, produces a signal which is representative of the quantity of vapor flowing from the reboiler section upwardly into the fractionation section. This signal is transmitted to heat-varying means, whereby fuel input to an external reboiler heater is regulated in response to the quantity of vapor flow.

Abstract: An apparatus for catalytically cracking hydrocarbons comprising a riser reactor having a plurality of catalyst injectors positioned along the length thereof. Adjacent to and upstream of certain of the catalyst injectors, cyclone separators are connected to the reactor so that fluid which contains a partially converted or cracked hydrocarbon and catalyst pass therethrough for separating the catalyst from the fluid with the fluid being returned to the reactor. Fresh catalyst is introduced into the fluid after same exits the separator to continue the cracking process. Steam can also be introduced into the reactor adjacent the catalyst injectors.

Abstract: A hydrocarbon stream comprising benzene is stripped at a high temperature to allow passage of the stripper bottoms stream into a clay treating zone without further heating, and the effluent of the clay treating zone is then exchanged against the feed stream to the stripper column to recover heat. Operation at the optimum clay treating temperature is achieved by adjusting the amount of the stripper bottoms stream which is split off for cooling by heat exchange against the feed to the stripper column. The cooled split-off portion is then admixed with the remaining high temperature portion.

Abstract: Heat balance of a fractionation column is maintained through the utilization of differential temperature sensors located at selected points in the height of the column. Signals representative of three delta-T's are employed in regulating the quantity of reflux to the rectification zone and the enthalpy (heat-input content) of the reboiled liquid bottoms stream. With respect to the former, two differential-temperature signals are used; these result from four temperature sensors vertically-spaced along virtually the entire height of the fractionation column.

Abstract: This invention relates to a process for producing alkyl adamantanes by reacting tetracyclododecanes and hydrogen in the presence of a specific catalyst.

Abstract: The method consists in preparing from the crude petroleum being processed a representative cut constituting a vaporized fraction having a known yield, in plotting the TBP curve of the cut by chromatographic analysis and by integration of the quantitative signal produced as a result of the analysis. The information obtained from the analysis is processed in order to operate a control unit for generating signals which serve to adjust the rates of withdrawal of the cuts at different predetermined levels of the column.

Abstract: Adjustment and control of a product fraction stream and especially gas oil are effected by a control unit after processing information supplied by an analyzer which takes a direct measurement of the temperature of filtrability of the stream and by detectors which deliver signals representing the flow rate of the gas oil withdrawn, the rate of withdrawn of the next higher product stream, the flow rate of the crude petroleum being processed, the flow rate of the stripping vapor and of the next lower product stream, and the slope of the distillation curve of the crude petroleum in the gas oil zone.

Abstract: Overflash within a withdrawal zone of a complex fractionating column is monitored to provide a control characteristic related to the efficiency of the fractionation column, and associated processes linked to the column. To accurately monitor the overflash, notched weir means including an upright wall means, is positioned at the intersection of the withdrawal tray and the downcomers connecting the former with a lower, adjacent fractionating tray. Differential pressure measuring means is also provided with sensing means in the vicinity of the notched weir means. The differential pressure measuring means produces a signal characteristic of said overflash. A complex controller means, external of the column, generates correction operators in response to said signal. Respective control means regulate column feed and withdrawal streams in response to said correction operators and thus maintain a pre-selected material balance within the column.

Abstract: From the values for the recycle oil feed rate and the fresh oil feed rate of a hydrocracker a material balance conversion computation is carried out resulting in a material balance conversion signal. From the values for the hydrogen flow rate the temperatures and the pressures thereof and the total oil feed flow rate and the flow rate and temperature of the material leaving the hydrocracker, an enthalpy balance conversion computation is carried out resulting in an enthalpy balance conversion signal. The material balance conversion signal and the enthalpy balance conversion signals are computed into a control signal. The control signal regulates the temperature of the total charge to the hydrocracker to maintain the actual percentage conversion at a desired value.

Abstract: A control system for regulating the reaction zone temperature in a process for the acid-catalyzed reaction of an isoparaffin with an olefinic feed stream containing mixed olefins. Hydrocarbon analyzers produce process output signals which are representative of composition characteristics of the fresh olefinic feed stream and the liquid alkylate product. These process output signals are transmitted to computer/comparator means which develops an output signal as a function thereof. The computer output signal is employed to adjust the reaction zone temperature to obtain the optimum consistent with a given feed composition and desired alkylate product quality. The control system rapidly compensates for continuing changes in feed composition which, at a fixed reaction zone temperature, would otherwise adversely affect the alkylate product quality.

Abstract: Maximum removal of asphaltic material, including high molecular weight metallic contaminants, from a hydrocarbonaceous charge stock is achieved through the utilization of a solvent extraction zone provided with direct top-heating facilities in the upper portion thereof. The top-heating section of the extraction zone is divided into two liquid-collecting zones in partial open communication with each other. A portion of the liquid is removed from the lower liquid-collecting zone, increased in temperature and returned to the extractor in the upper liquid-collecting zone. The flow rate of liquid withdrawn from the lower zone is controlled in response to the differential pressure between the two liquid-collecting zones.

Abstract: A heat exchange method and flow control system for a hydrocarbon conversion process having two reactors in series which allows efficient heat recovery and effective process control under widely varying process conditions. The hydrocarbon feed stream is divided into three streams. In the preferred embodiment, the first stream is not heat exchanged and is controlled along with the preheater heat supply by a split range controller activated in response to the temperature of the stream entering the first reactor. The second stream is heat exchanged with the effluent of the first reactor and flows at a rate controlled by its temperature after this heat exchange. The third stream is heat exchanged with the effluent of the second reactor and flows at a rate such that the total of all three streams is the desired capacity for the unit. A hydrogen recycle stream is proportionally divided between the second and third streams by a ratio control means.

Abstract: The reboiler temperature of a depropanizer tower is controlled as the function of the propane content of the feed to the depropanizer tower and of the gasoline provided by the tower in accordance with a control signal. The Reid Vapor Pressure of crude oil feeding a flash tower is determined from the propane content of the depropanizer feed while the Reid Vapor Pressure of the gasoline is determined from the gasoline propane content. A control unit includes a network which determines a change in the Reid Vapor Pressure as the quality of the feed crude oil to the flash tower changes. When the change in the Reid Vapor Pressure exceeds a predetermined limit, the network provides a feed forward signal corresponding to a desired temperature associated with the new Reid Vapor pressure. The feed forward desired temperature signal is determined in accordance with the equations hereinafter disclosed.

Abstract: A system for controlling the hydrogen/hydrocarbon mole ratio in a continuous hydrocarbon conversion process wherein the hydrocarbonaceous feed stock is catalytically reacted in a hydrogen atmosphere. Applicable to both hydrogen-consuming and hydrogen-producing processes, in which the reaction zone effluent is separated to provide a liquid product phase and a hydrogen-rich vaporous phase, a portion of the latter being recycled to the catalytic reaction zone, the control system affords improved overall operation of the particular process in addition to increased catalyst activity and stability. Analyzers are utilized to monitor composition characteristics of the charge stock and liquid product, and the hydrogen concentration of the vaporous phase recycled to the reaction zone.

Abstract: A control system controls the flow rates of waxy oil and solvent entering a dewaxing unit so as to control the viscosity of a chilled slurry mix or waxy oil and solvent provided to a filter in the dewaxing unit. The dewaxing unit includes valves controlling the flow rates of the solvent and waxy oil being provided to the chiller. The filter provides a dewaxed oil and solvent mixture and wax. Using the equation hereinafter mentioned, the control apparatus utilizes the sensed refractive index of the solvent, the sensed viscosity of the waxy oil, the sensed flow rates of the solvent and the waxy oil, and the sensed filtering temperature of the chilled slurry mix to generate a signal corresponding to the viscosity of the slurry mix provided to the filter at the filtering temperature. The viscosity of the chilled slurry mix is controlled within predetermined limits by a generating signal corresponding to the dilution ratio of the solvent to the waxy oil.