US2306606A - Apparatus for determining the rate of hydrocarbon conversion - Google Patents

Description

APPARATUS FOR DETERMINING THE RATE OF HYDROCARBON CONVERSION J, H. HIRSCH Dec. 29, 1942.

Filed March 21, 1939 Q. Q N M w ww hm mm A 3 am mm N .ww L \N. (5 mi II R E m a 1 A, v w. m 5 WW M ww q a l l l l ln ld MN S: Q N v SW g Q L Y Patented Dec. 29; i942 Arraasrus' roa-nmnmmmom BATE, or maocaxnou coxvmtsron Joel mmmh, NewYork, N. 1., assignor to De Flores Engineering 00., Ina, Hartford, Com, 7 a corporation or Connecticut Application March :1, 1939, serial No. 203,221

1 Claim. (c1. la-'51) This invention relates to an apparatus for determining or controlling the rate of cracking or conversion or hydrocai'bonfluids.

- In the conversion of higher boiling hydrocaricons to lower boiling hydrocarbons to form motor fuels, it is desirable to rapidly determine the effectiveness of the process to determine the rate iractionating system.

ously affected and to a usually indeterminate ex-' tent by changing reflux rates in the towers'of the Furthermore, when two or more cracking zones discharge into a single i'ractionating system, gas

rate from the unit becomes meaningless as a measure 'orthe. extent of conversion in the indiat which the conversiontakes place. Orhavins a certain rate of conversion of hydrocarbon fluid' established, it is desirable to control and maintain the rate of conversion.

For example, when a higher boiling hydrocarbon, such as gas oil, is to be converted into lower boiling hydrocarbons containing gasoline constituents or motor 'fuel constituents, it is passed through a heater and generally heated to a relatively high temperature up to about 1290' F. or higher and under a superatmospheric pressure up to about 1000 pounds per square inch or higher. Thehigher boiling hydrocarbon in through the heater is maintained under suitable.

temperature and pressure conditions for a time suflicient to effect the conversion into lower boilinghydrocarbons. The products of conversion pass through a transfer line to a separator usually under lower superatmospheric pressure to separate vapors from liquid residue. The vapors are then passed to a fractionating zone preferab y under superatmospheric pressure to separate condensate oil from a desired lighter fraction.

The rate or conversion is usually expressed as the volume per cent of the gasoline produced, based onthe volume of charge-of hydrocarbon fluid introduced into' the heater; but it might be equally well expressed as the'weight percent of gas plusgasoline formed or the weight Per cent as formed, since for any given character of vidual zones. Hence, over-cracking may take place in one zone and under-cracking in another without being detectedby the gas rate from the unit,.which measures only the combined elect. Moreover. with existing means of control the extent of conversion tends. to be an average conof crackin dltion with respect to time rather than'the maximum attainable without boxin of the apparatus; since'only a 2 I". change in effective tem-.

perature produces about a 8% change in exte nt For example, when a cracking coil is operating at an average conversion per pass or rate of conversion of 20%, the conversion per pass may vary from moment to moment between fairly wide limits, such as 18% to 22%. Assume in this example that it is the 22% rate which limits the 5 operation by cokingthe apparatus. Maximum capacity and fuel economy would be attained by operating Just below the maximum conversion or the-22% rate at all times. The invention dis'-' closed herein makes this possible. tion mayrbest be.characterized as one which effects its control by measuring "continuously and almost instantaneously the net result of the conversion operation rather than some associated heater feed stock and set of operating conditions 'these three quantities are inter-related and may behexpressed as mathematical functions of each 0 er. c

Some prior methods of controlling hydrocar-, bon conversion processes utilize the temperature or cracking, arrangements must be 40 of the stream leaving theheater and/or the rate I of fixed gas from the gas separator at the end of the fractionating system. Heater outlet temperature possesses serious disadvantages as a basis for controlling these,operations in that 'the extent of conversion may varylwhile the outlet temperature remains constant, due to shifting of in the heater flow. Gas rate is unsatisfactory in that there is a considerable time lag between the cracking zone and the gas separator and the pro ty, such as heater outlet temperature,

- which although related to extent of conversion is not necessarily a true index thereof.

It sampling tests are to have any value in determining or controlling the rate of conversion where-' by such kests may be made continuously and quickly. My inventionrincludes apparatus and amethod whereby the rate. of conversionof the hydrocarbon fluid may be quickly, accurately and continuously determined by measuring the rate of production or gas resulting from'the cracking I or conversion operation. Or my invention may be used in the control of a conversion process to maintain a desired rate of conversion. My invention may be used for determining the extent temperatures or pressures at intermediate points 9 ofconversion operations generally where hydro carbon .fluids are-to be converted into higher. or

- lower boiling hydrocarbons and in the control of such conversion operations. According to one form .of my rate or gas discharge 1 m t mfg;- -1.5.;- substantially continuous, stream of conversion My inveninvention a small,

cracking zone (not shown).

' separator. is maintained substantially constant and the temperature of the products of conversion v introduced into the separator is maintained substantially constant.

In the separator, gases are separated from liquid. The liquid is withdrawn from the bottom of the separator at a substantially constant rate. The gas leaves the top of the separator and is measured by passing it through a flow meter. Vith the liquid flow rate constant,- the gas flow rate represents the gas produced per unit of liquid separated in the separate The volume of'gas produced is measured and from this it is a relatively easy matter to determine the volume per cent gasoline production or conversion per pass obtained. Data are available to show that having a known oil stock and converting it under known pressure and temperature conditions, the amount of :gas produced will be in proportion to the amount of gasoline produced.

The cooled and condensed products of conversion are then passed through line 2| and through a line filter or strainer 22 for removing any solid introduced into a chamber 25 adjacent a float controlled chamber 36 and then through line 31 to separating chamber 28 wherein gases are separated from liquid. The float controlled chamber 28 and chamber 25 willbe described in great- The thermostatic device er detail hereinafter. 34 is connected by means of an electric circuit 42 with a meter controller 40. The control device is provided with an air pressure supplyline 43 and with a discharge line 44 for applying air pressure to a diaphragm 28A which operates the valve 2'. The controller regulates the pressure applied to the diaphiagm in response to the thermostat and controls the valve 26 to regu- My invention is especially adapted formeasur- I ing the conversion rate or controlling the conver: sion rate in a conversion operation where two or more conversion zones are used with a single fractionating system as an apparatus constructed to embody my invention may be used with each conversion zone and the conversion rate of each conversion zone may be, measured or controlled.

' The drawing represents a diagrammatic showing of one form'oi' apparatus adapted for use in practicing my invention. is not to be limitedto the apparatus shown as other apparatus may be used. I

' Referring now to the drawing, the reference character l0 designates a pipe in which hydrocarbons are subjected to cracking or conversion or a transfer line which is adapted to conveyhot products of conversionleaving a conversion or According tomy invention a small amount of hot productsof converstream through line I 2 which communicates with the pine l0. Theproducts of conversion are at a relatively high temperature and it is necessary to cool them and reduce the temperature to condense normally liquid constituents and separate them from gases. The hot products of conversion are passed through line l2 and are cooled to below cracking temperatures byf'a shock cooler ll However, the invention.

sion is preferably continuously removed as a which surrounds a portion of-line l2 and which is provided with an inlet II and an outlet I. for cooling fluid. Water is preferably used as a cooling medium in cooler M for initially cooling the hot products of conversion to a relatively low temperature.

The partially cooled products of conversion are then passed through a valve is in line 2| and are then passed through a condenser-:22 for er cooling the products of conversion to a d ired substantially constant temperature. used as a cooling medium in the condenser 22 and is passed through line 2| provided with a control valve 28 and an outlet 20. The control valve 2' is operated by a temperature control device, as

Water is.

late the amount of cooling water used in condenser 22 forTzooling the products of conversion and for maintaining the temperature of the products of conversion substantially constant. A drain pipe I may be provided in line 33 below strainer 32, if desired, but no liquid should be withdrawn through pipe 45 at any time while'the apparatus is being used for measuring the rate of conversion. Instead of controlling the valve 26 by air pressure, as illustrated, the valve 26 may be controlled by electrical means or other means. r s

For example, if the products of conversion passing to the separating chamber 3! are at too high a temperature, the temperature controldevice 40 will operate the controlv mechanism on the control valve 28 to cause more water topass through the condenser 22. If the products of conversion are at too low a temperature/the temperature control device will regulate the valve 20 so asto provide less water for the condenser 22. In this way the products of conversion are introduced into the separating chamber is at a substantially constant temperature. F-

The float controlled chamber 2 is provided with the smaller chamber '25 which is separated from the main portion 46 of float chamber 38 by means of a wall 41. The cooled,p'roducts of conversion from line 23 are introduced into smaller chamber 1! and then through line 31 into separating chamber ll as will be presently described in greater detail.

A float. controlled valve l8 cooperates with 7 N or 5. When the level of liquid in chamber I. rises, the level of liquid in main portion 46 oi.

, control chamber 36; Line I4 contains liquid whereas line 58 contains gas. There, is no substantial flow in either line float control chamber 36 also rises and valve 48 is.

moved closer to valve seat-50 and greater throttling takes place at parts 48 and i0 and a smaller amount of conversion products is introduced into smaller chamber 35 and hence to separating chamber 28.

The float 52 and its associated parts will now be described. The float 52 is provided with a I provided with a connection a to the pipe m float arm to which is pivoted at inside the I upstream from the orifice I33 and with a comet;-

main portion 43 of thefloat control chamber 33. "A lever arm 33 is rigidly connected with the float arm 33 to provide a bell crank construction. The

lever arm 33 is pivotally connected to a valve stem 33, the lever arm being provided with a slotted opening through which the valve stem extends. The valve stem extends into smaller chamber 33 and is provided with the valve member 43 at its one end which is adapted to cooperate with the valve seat 33 provided atthe entrance to smaller chamber as above described to control'the amount of products of conversion being introduced into the smaller chamber 33 through line 33. The valve stem 33 .ex-..

tends through opening 33' in separating wall 31 and the wall 31 with its opening 33 forms a guiding and bearlngmeans for maintaining the. valve member 43 in alinement with valve seat 33.

The valve stem 33 is adapted to slide freely in the 3 opening 33 in separating wall 31.

By this float valve construction the inflow and outflow are balanced. With liquid outflow from variations in the level of the liquid in the chamber 33. with the floa't controlconstruction a body of liquid is normally maintained in main portion 33 of float chamber 33. The full transfer line pressure 'may be carried up to the float controlled valve member 43. The pressure in the float chamber 33 is maintained substantially constant, preferably at a lower pressure than transfer line pressure: as will be hereinafter described in greater detail. e

The products of conversion from smaller chamber 33 are passed through line 31 and are preferably introduced into an intermediate portion of separating chamber 33 and preferably tangentially as at 13 to me inner wall of chamber 33 to assist in separating entrained liquid from the gases. The line 33 from main portion 43 of float controlled chamber 33 communicates with the separating chamber 33 at a higher point as at 12.

A-gauge glass construction 13 'is preferably provided on separating chamber 33 to provide visual means whereby the liquid level may. be observed.

The gases in the separator 33 are passed overtion I II downstream from the oriflce. The flow control device is also-provided with an air pressure supp y line I33 and a discharge line I33 for applying air pressure to a diaphragm I35 which operates a valve I33 in the line I32. Preferably the separating chamber 33 held substantially conthe control valve I 33 is placed after the meterin device I 33 to obviate. any possibility of errorin measurement due to gassing. The desired rate of flowis maintained by the flow control device 33.

The flow control device 33 is set for a predete'r-- mined rate of flow-of liquid and variations from this flow are compensated for by means of the control valve I33. Instead of controlling the valve-I33 by air pressure as illustrated, the valve I33 may be controlled by electric means or other means. I

After passing through the metering device I33, the liquid passes through the line 132 into the fractionating equipment or other. equipment in the refinery, or into the emergency line, as desired. Whenever it is desired to determine the properties of the gasoline in the liquid passing through line I32, this can'be doneby withdrawing asample of the liquid through line Ill and subjecting it to laboratory tests.

The gas passing overhead from the separator 33 'throughline 32 flows through an orifice H3 in the line 32. A gas rate meter I I3 is in communication with the line 32 through a'line II1 upstream of the orifice and a line I I3 downstream of the orifice in order to measure the amount of gas produced during the conversion operation. After passing through-the metering device I I3, the gas flows to fractionating equipment, tar stripper accumulating drums or other equipment in the refinery to recover any desired constituents thereof. Samples of the'gas for laboratory tests may be withdrawn at I24. While the gas passing through line 32 may be passed to a zone of substantially constant pressure such as those just mentioned above so as to keep the pressure on head through line 32 and the liquid is withdrawn through line 33. Line 33 is provided for draining the float chamber and separating chamber 33 but no'liquid should be withdrawn. through .line 33 at any time while the apparatus is being" used for measuring the rate of conversion.

The upper portion of the. separating chamber 33 is provided with suitable contact elements such as Rasch'ig rings 34 or the like supported on a tained substantially constant and, in order to produce this result, a flow control device 33 is provided. The flow control device 33 cooperates. with anvzorifice l33'arranged in line I32 through hich passes the liquid withdrawn from the botton of separator 33. The flow control device is the rate of flow of liquid from-the separating chamber 33 is main-" from the bottom of the separating chamber 33 ing chamber 33. Also the rate of flow of liquid the float chamber 33 and separating chamber 33.

substantially constant, I prefer to use a pressure controlling valve I23 in gas line 32. Pressure controlling valve I23 is placed after metering device H3 in line 32 and is operated by a diaphragm I21 to which pressure-is applied through a line I23fcommunicating with Separatingphamber 33. In this way the pressure in the chambers 33 and 33 is maintained substantially constant.

In the invention as disclosed, the pressure and temperature are maintainedsubstantially constant in float controlled chamber 33 and separatwithdrawn .from the separating chamber 33 is maintained constant. Knowing the pressure in the conversion apparatus and the nature of the .charging stock, and maintaining the temperature suitable for conversion, the amount of gas prdduced will be a direct indication of the amount of conversion obtained in the charging stock. In some instances it may be desired to measure the rate of flow of liquid and the rate of flow of gas from .the separating chamber to obtain the amount of conversion.

A specific example of the operation of my invention will now be given' but it-is to be understood that I am not to be restricted thereto. The example is merely by way of illustration to further explain my invention. At first-I will briefly de scribe a general conversion operation and separation of the products of conversion and then I will describe the operation of my invention in con nection with such a conversion operation. In this brief description apparatus will be referred to which is notshown in the drawing except transfer line l0.-

In a conversion operation, a charging stock such as Mid-Continent gas oil having an A.P.I. gravity of 30 is fed to a cracking unit, mixed with unconverted gas oil recycle stock and passed through a heating and conversion zone; wherein it is maintained under superatmospheric pressure of from 500 to 1000 pounds per square inch and heated to a temperature of 800 to 1000 F. The products of conversion leave the conversion zone through the transfer line l0, passing to a separator or evaporating chamber, operated at a lower superatmospheric pressure and'a lower temperature, where liquid residue or cracked fuel oil is separated from vapors by condensation The cracked fuel oil is withdrawn from the bottom of the separator to storage. The vapors pass overhead into a second chamber or fractionating tower. In the fractionating tower gas oil recycle.

stock which has not been converted into any of the products eliminated from the cracking unit (i. e., gas, cracked gasoline, or cracked fuel oil) .is separated from the gas and gasoline by fractional condensation and passes to the bottom of the fractionating tower. Gas and gasoline pass overhead from the fractionating tower and then through condensers to a gas separator where the gas is separated from the gasoline, these materials then beingeliminated from the conversion unit to storage or for subsequent treatment. Gas oil recycle stock from the bottom of the fractionating tower mixes with fresh gas oil charging stock'and passes again through the heating and conversion zone.

A small portion of the products of conversion passing through the transfer line I0 is preferably continuously removed from the transfer line the condenser 22. During cooling, the normally liquid hydrocarbon constituents are condensed The cooled'and condensed products of conversion including gases and liquid are then passed through the line strainer or filter 82 and then through, line 33 to the small chamber 35 of float controlled chamber 85. The cooled and condensed products of conversion then pass through line 31 to separating chamber 38 wherein gases are separated from liquid. r

In passing through line 83\the 6ooled and condensed products of conversion pass in coiitact with the thermostatic device 84 and their temperature is measured. The thermostatic device 34 is connected with the control device 40. The temperature of the cooled and condensed products of conversion introduced into" the chamber 35 of the float controlled chamber 36 is maintained constant at a temperature between about 90 F. to 125 F., preferably about 110 F. If the temperature of the conversion products is too v high, the temperature control device ll in response to thermostatic device 8| will actuate the control device on valve 28 to introduce more cooling water into the condenser 22. On the other hand, if the temperature of the products of conversion passing through line 83 is too low, thenormally maintain a body of liquid in separating chamber 38 'and main portion 46 of float chamber 36. In the separating chamber 88 the pressure is maintained at about to pounds per square inch, preferably about 50 pounds per square inch. The pressure is maintained constant in chamber 38 by means of the pressure control valve I28 in line 82. Higher pressures may be used in chamber 88 and higher temperatures may also be used.

In practice it is convenient and desirable but not necessary to so set the liquid flow rate that the total gas plus liquid equals 100 pounds per hour or some unit quantity in which case the gas meter will read weight per cent gas directly.

The weight of the gas formed divided by the sum of the weight of the gas formed and liquid separated gives weight per cent gas. Also in the example given below where the weight of gas charge fed to the. heater is 3%. It is not necessary to know the rate of charging feed stock to the conversion zone in-order to obtain the per cent conversion with my invention.

The liquid separated in the separating chamber 38 is withdrawn therefrom at a substantially constant rate of about 97 pounds per hour and this rate of flow of liquid is maintained substantially constant by means of fiow control device as which scalar-es the control valve I08 in line I02.

The gases passing overhead from the separating chamber 38 are then measured by passing through the metering device I i6 and the amount of gas is re orded .or read on the gas meter, H8.

For example, a gas flowof about .3 pounds per i being obtained. J

From previous data it is known that there is a definite relation between the amounts of gas and gasoline formed when converting a known cracking stock at various operating conditions. For

example, when. converting a 30 A. P. I. Mid- Continent gas oil in a cracking process of the type described above, 4% of gas by weight would valve 28 will be operated to 'cut down the flow of cooling water through the condenser 22.

correspond to about 28 volume per cent of gaso-. line or conyersion per pass through the conversion zone and 2% of gas by weight would correspond to about 14% of gasoline by volume.

For the same feed stock at a given operating pressure in. the conversion zone these values of amounts of gas and gasoline produced will vary with theconversions per pass, and with these different values a curve may be drawn wherein volume per cent gasoline formed or conversion per pass is plotted against weight per cent of gas pr duced. Different curves may be drawn for d erent operating pressures for the same feed stock and diflerent curves may be, drawn for different stocks fed to the conversion zone;

Having these curves and knowing the character of the feed stock and pressure in the conversion zone, and measuring the weight per cent of gas produced, the curves will immediately give the volume per cent gasoline produced or conversion per pass. From the above it will be seen that the relationshi between volume per cent of gasoline produced and the weight per cent 'of gas My device is more sensitive than devices in comproduced is independent of the temperature.

Knowing the pressure in the conversion zone and knowing the feed stock and measuring the weight per cent gas produced is all that is necessary to obtain the conversion perpass.

Data are available, and some have been published, which correlate the gas-gasoline ratio for various cracking stocks (i. e. the weight of gas formation per unit weight of gasoline iormation) with the physical properties of-the oil charged to the cracking zone and the operating pressure maintained therein. Since my invention gives the weight per cent gas produced, it is only-necessary to know in addition the gravity and A. S. T. M. distillation of the oil charged to the cracking zone and the operating pressure I short periods at three or four difierent cracks per pass or conversions per pass, evaluating samples of the liquid withdrawn from the separating chamber 38 for per cent gasoline by laboratory fractionation and plotting these values against weight percent gas as shown by the gas rate meter H8.

In the specific example my invention has been described as applied to the sampling of products from the transfer line through which the products of conversion leave the conversion zone. However, the sampling line l2 may be connected with the conversion coil at any desired point in the furnace and a stream of conversion products withdrawn and passed through my apparatus to determine the extent of conversion of the charging stock to gasoline at any desired point in the conversion coil or at various points in the conversion coil to determine the extent of conversion of the charging stock as the charging stock passes through the conversion coil. 7

In addition, knowing the characteristicsof the charging stock and where a particular conversion per pass is desired to be maintained, my invention may be used to control the conversion unit and maintain a certain conversion per pass of the charging stock to gasoline. For controlling the conversion unit it is unnecessary to know the conversion per pass in termsof per cent gasoline formed as the only factor of importance according to my invention is to know as quickly as possible when a change in conversion per pass has occurred. For this purpose weight per cent of gas alone is just as good a criterion as volume per cent gasoline.

My invention can also be used as a reset mechanism on a conventional temperature controller.

mon use for control purposes such as transfer line temperature controllers. For example, an increase of about 2 F. in theefiective cracking temperature would produce about 6% increase in the gas rate which is easily measured by my invention.

My invention is especially adapted for measuring the effectiveness of conversion or the conversion per pass of a plurality of conversion zones where such conversion zones are associated with and discharge into a single fractionating system. In this case separate apparatus for determining or controlling the extent of cracking will be used with each conversion zone.

While my apparatus is preferably continuously operated and a stream ofconversion products continuously withdrawn through sampling'line l2, it is to be understood that, if desired, the invention ay be used intermittently and a stream of conversion products may be withdrawn through line I! intermittently.

My invention is also adapted for use in determining the extent of conversion or for controlling the conversion where other conversion operations such as vis-breaking, reforming. as polymerization, gas reversion, etc., are to. be measured'or controlled. In the case of gas polymerization,

the gas from thetop of the separator 38 is withdrawn'at. constant rate and the liquid withdrawn through line I02 then constitutes the measure of the extent of conversion.

While I have shown one form of apparatus V embodying my invention it is to be understood that this is by way of illustration only and modifications and changes may be made without digressing from my invention.

I claim:

In apparatus for determining the rate of gas formation capable of directly reflecting the extent of cracking in a conversion apparatus wherein hydrocarbons are subjected to conversion, the combination with said conversion apparatus of a sampling line for withdrawing a sampleof the products of conversion, means for cooling the withdrawn products to condense the normally liquid hydrocarbons, a separating chamber in' communication with said cooling means and adapted to separate gases from liquid, means-for controlling the amount of cooled products introduced into said'separating chamber. means for regulatingthe cooling applied to said withdrawn products soas to maintaih a substantially constant temperature'in the-separating chamber,

means for maintaining a substantially constant pressure in the separating chamber, means for withdrawing liquid therefrom at a substantially constant rate, a gas outlet from the separating chamber and means for measuring the amount of gas flowingtherein.

\ JOEL H. 'HIRSCH.

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