US2892769A - Automatic burner fuels and process of making them - Google Patents

Description

United States Patent 9 2,892,769 AUTOMATIC BURNER FUELS AND PROCESS OF'MAKING THEM Raymond L. Frazier, Concord, and Robert D. Harrison, Orinda, Calif, assignors to Tidewater Oil Company, a corporation of Delaware Application September 2, 1953 Serial No. 378,102 4 Claims. (Cl. 208-15) This invention relates to liquid burning fuels for heating devices such as automatic fuel burners. More particularly, it relates to burner fuels comprising, as an important component, cracked hydrocarbon distillates in the 450 F.-700 F. boiling range.

The fuel burners referred to herein are those in general use, for example, as hot water heaters, heating furnaces for homes and other buildings, bakery ovens, and so forth. Typical of the automatic burners to which the fuels of the present invention are applicable is the home water heating unit. One example of this type of heating unit is fired by an atomizing burner at a rate of 1 /2 gallons of fuel per hour. This unit is operated to heat water from room temperature to 160 F. at the rate of 80 gallons per hour.

These fuel burners are to be distinguished from pottype burners and from residual fuel burners which also may be of the forced draft type. The characteristic difference found in the fuel burners of the type intended herein is the provision for atomizing fuel in a fine spray. This operation requires that the fuel be passed through small orifices after passage through a screen which prevents clogging of the aforesaid orifices by oversize particles. Furthermore, the fuel burners considered herein may be distinguished from residual fuel burners in that the former are designed to use hydrocarbon distillates as fuels and are unsatisfactory for burning residual materials.

Storage of distillate fuel oils is often handicapped by the formation of undesirable materials in the fuel oils. After prolonged storage, they may tend to discolor and insoluble material then precipitates in the fuel oils, leading to the formation of sludge. These products cause clogging of screens, conduits and other-parts of burners.

An acceptable fuel for use in oil burners must, of course,

be free from any tendencyto clog filter screens and the numerous fine passages and openings present in fuel oil burners. The fuel oil used in such equipment can inter! fere with the performance of various parts in several ways, among which are clogging, gumming, and corrosion. One type of sediment which will cause clogging and otherwise be detrimental togood performance in-.

cludes materials such as sand, dirt, iron rust, dust, water, emulsions and miscellaneous debris. This type of sediment may be avoided simply bykeeping the original oil clean and free from extraneous insoluble materials. A second type of sediment is that which may form in the fuel oil on storage. Such sedimentis an organic material originating mainly in oxidation and polymerization reactions in the oil. The presence of oxygen or air is known to further these reactions, along with exposure to light. These sedimentary materials may be very finely divided, clogging small openings and fine pores of filters; and, in some cases coagulating 'inthe form of coarser sediment forming large deposits throughout the fuel burning equipment.

While the tendency of fuels to clog filters varies with difierent fuels, it is generally recognized that neutralized straight run products have littlev inclination toward precipitate formation although cracked distillates readily dev'elop large volumes of precipitates after only a relatively short storage period. Furthermore, cracked distillates tend to form reaction products with the copper and copper bearing screens and filters. These products tend to coat the wires so as to clog or reduce the size of the open mesh of the screen such that even fine insoluble matter will clog the openings. Moreover, copper and iron are known catalysts for sludge formation in unstable fuels.

While straight run products provide excellent quality burner oils resulting in their widespread use for this purpose, the advent of cracking processes in the petroleum refining industry has presented the problem of adapting cracked products as satisfactory substitutes for the diminishing supply of straight run materials. Moreover, it has long been preferred in modern refinery operations to charge as much feed as possible to cracking units in order to meet increased demands for aviation and automotive gasolines. As generally practiced in modern refineries the charge to catalytic crackers is straight run gas oil distillates of varying boiling ranges, e.g. 400 F. to 750 F. Consequently, the supply of straight run gas oil for use in automatic fuel burners is markedly reduced. Furthermore, with the present day emphasis on cracking operations in the refining of petroleum there has emerged a need for the development of new uses for the many byproducts of gasoline manufacture.

Modern catalytic cracking comprises several well known processes. For instance, one of the most important processes, known as fluid catalytic cracking, utilizes a fluidized catalyst bed in intimate contactwith hydrocarbon vapors in the reaction zone. Temperatures are maintained in the range of 850 F. to 1000 F. with a slight increase over atmospheric pressure. For purposes of illustration the present description will be more particularly described in relation to fluid catalytic cracking, although analogous results can be expected from other types of catalytic cracking processes. Other catalytic cracking processes well known in the modern cracking art are moving bed processes known as Thermofor Catalytic Cracking and Houdriflow Catalytic Cracking. The reaction temperatures in all catalytic cracking operations are generally in the aforementioned range and the catalyst in general use throughout the industry is a silica.- alumina composition comprising either acid treated Montmorillonite clay or a synthetic silica gel material having temperature and time limits and at regulated pressures to produce maximum yields of gasoline With minimum coke formation. For example, a typical thermal crack ing operation takes place at about 950 F. The pressure at furnace inlet is about 400 psi. and at the outlet,

about 200 p.s.i. Provision may be made for recycle of gas oil fractionated from the reaction products; thus the charge to the furnace may be, for example, 520v gallons per minute and the charge of raw feed stock being gallons per minute. A typical thermal cracks.

ing operation will produce about 20% raw pressure distillate (cracked gasoline), although amounts ranging from about 10% to 22% may be produced under varying conditions of cracking intensity and charge stocks.

In the absence of a sulfuric acid treatment, which is' often economically disadvantageous, catalytically cracked petroleum hydrocarbons have long been considered unsatisfactory as burner fuel blending components. These materials have a high aromatic content, poor burning characteristics, and are relatively unstable. Although caustic treatment of catalytically cracked materials will substantially reduce precipitate formation on storage,-

such treatment does not overcome the aforementioned disadvantages inherent in these materials.

Likewise, the quality of thermally cracked products per se does not approach that of straight run materials. When used as automatic burner fuels. This is generally caused by the presence of sulfur and other contaminants which can not be removed economically by conventional means.

In contrast to the art which teaches that catalytically cracked products are not easily converted into useful burner fuels, we have found that goes oil, produced by thermally cracking heavy gas oil (materials boiling in the range of 550 F. to 900 F.) obtained from catalytic cracking operations, is an excellent blending component for burner fuels. A typical heavy gas oil suitable for this purpose is slurry oil obtained in the catalytic cracking operation. The term slurry oil is used to indicate that heavy gas oil which is carried over from the catalytic reactor to the fractionator along with contaminating catalyst fines. It is sometimes referred to as decanted gas oil after it has been separated from the catalyst particles and a typical example has the following analysis:

Gravity, API 12.2 Flash Point, F. 295 Pour Point, F. 45 Viscosity, S.U. at 100 F. 220 Sulfur, percent 0.72 Aromatics, percent 58.0

The other blending component may be, for example, a straight run product boiling in the diesel oil range (approximately 450 F. to 700 F.). This eliminates the cost of acid treating catalytically cracked materials in order to produce a satisfactory burner oil. Instead it provides a means for upgrading heavy gas oil while at the same time producing still more gasoline by thermal cracking.

In accordance with the invention, it has been found that thermal cracking changes the characteristics of catalytically cracked stock greatly improving its burning and storage characteristics. This is quite unexpected in that it is common knowledge that either thermal or catalytic cracking injuries the burning-and storage characteristics of petroleum oils and they are not generally considered satisfactory for burner fuels unless they are given some radical treatment such as acid treating. Consequently, while the conventional practice is to use as cutter stocks (diluents used to reduce viscosity and pour point of heavy crude oil and residuum) the gas oils which have undergone catalytic cracking, this invention contemplates their use as burner fuel blending components.

The charge stock to a fluid type catalytic cracker usually consists of straight run gas oils and generally includes heavy distillates prepared by vacuum distillation of straight run residuum and/or heavy crudes. During the catalytic cracking of this charge stock an increase in aromatic content will be produced, accompanied by an increase of carbon to hydrogen ratio in the products. The catalytic products are usually transferred to a fractionator wherein appreciable amounts of catalyst fines accumulate in the bottoms material. This slurried catalyst from the fractionator may be drained 0135, as for example, into a Dorr thickener wherein the heavy gas oil (slurry oil) is separated from the catalyst fines and decanted. The catalyst fines are then returned to the reactor, along with sufiicient heavy gas oil to allow for mobility. The present invention provides for charging the decanted heavy gas oil directly to a thermal cracking unit and products such as cracked gasolines (raw pressure distillates), gas oils and heavy fuels are formed during this thermal process. Following this, the gas oil, thus made by thermally cracking the heavy catalytic gas oil may then be blended in equal amounts with straight run gas oil of suitable viscosity, such as that used as fuel for diesel engines and commonly known as diesel fuel, to form good quality burner fuel. The invention contemplates blends containing between about and 50% of the doubly cracked gas oil with from about to 50% of straight run gas oil. r

A caustic wash of the thermal gas oil product may be advantageous especially when the gas oil contains phenols, cresols and other such materials. A typical caustic treat is 3% by volume of 10 Baum NaOH. Although excess alkalinity must be present during this treat, a wide range of strengths and rates may give a satisfactory product. While the product of our invention is suitable as a burner fuel, the invention does not preclude the addition of one or more inhibitors which have been developed for the purpose of improving stability. An excellent material for this purpose is Santolene H, a product marketed by the Monsanto Chemical Company and believed to be a high molecular weight amine. Some other suitable commercial additives are as follows: PL16l by El. DuPont de Nemours, SR158D by National Aluminate Corp., Paradine HO-2 by Enjay Corporation, Ionad 17 by Shell Chemical Corp., DR-1817 by Gamlen Chemical Company, and Pet-re-Nol by Norman Chemicals Inc. Varying amounts of Santolene H have been found satisfactory and a suggested quantity, based on economic consideration, is 0.025 volume percent.

Straight run stocks in the diesel oil boiling range, with or without caustic treatment, are preferred for blending with the gas oils prepared by the catalytic plus thermal cracking process described herein. Finished burner oils prepared in this manner provide a satisfactory substitute for straight run products and are far superior to blends of other cracked materials which have not undergone the added expense of H 80 treatment. The accompanying Tables I and H illustrate this comparison. Table I shows the results of standard physical and chemical tests performed on straight run (virgin) stock, on products from the examples included herein, and on catalytically cracked burner oil blends with or without inhibitor. The sludge formation test is performed by recycling the sample burner oil through a stainless steel screen of 200 mesh and at a temperature of about F. for 48 hours. The condition of the screen is then determined as to sludge formation thereupon. Table H shows the results of tests on an automatic hot water heater operating over a 10 day period at a rate of one and one half gallons of fuel per hour. The smoke meter test is a measure of the transmissibility of light in the burner stack, readings being taken at a standard distance from the exhaust port of the burner.

Our invention is further illustrated in the accompanying drawing representing a flow diagram of a preferred form of our process, in which a refinery crude oil is processed to yield blended burner fuel along with optimum yields of gasoline and other premium products. The crude oil enters the atmospheric distillation tower 1 through line 2. Overhead products leave tower 1 through line 3 and a portion of diesel oil boiling range side out passes to blending tank 4 through line 5, while another portion is charged to fluid catalytic cracking unit 6 through line 7. The bottoms product from tower 1, generally known as straight run residuum, is transferred by line 8 to vacuum feed preparation unit 9 where it is separated into overhead and side out products which pass to fluid catalytic cracking unit 6 through line 10, while straight run asphalt or deep flashed residuum is removed from preparation unit 9 through line 11 and generally disposed of as low grade fuel in equipment designed to burn such pitch-like oils. Cracked products from cracking unit 6 flow through line 12 into fractionating tower 13. Gasoline is distilled 05 through overhead line 14 while lines 15 and 16 provide for the removal of light and heavygas oil side cuts respectively. Heavy gas oil and minor quantities of catalyst fines are transferred from fractionating tower 13 through line 17 into Dorr thickener 18 wherein the catalyst fines settle out and are returned through line 19, with a small amount of slurry oil to provide for mobility, to the catalytic cracking unit 6.

The major portion of slurry oil is decanted from the Dorr thickener and charged through line 20 to thermal cracking unit 21. Cracked distillates pass through line 22 into fractionating tower 23 :from which cracked gasoline leaves through overhead line '24 while cra'cked gas oil is fed into blending tank '4 through line 25. Alternately, instead of line 25, .caustic treating unit .26 may be connected with fractionating tower 23 by means of line 27, and, with blending tank 4 by means of line 28. Line 29 allows for admission of caustic make up and line 30 allows for the "release of spent caustic to the sewer or for return to further use. Blending tank 4 is provided with line 31 for admission of inhibitor as desired. Drawoff line 32 allows for removal of finished product for sale and use as burner fuel. Lines 33 and 34 are provided for removal of bottoms products from fracfractionating tower 23 and thermal cracking unit 21, are provided for removal of bottoms products from respectively.

The following examples illustrate typical applications of the present invention to refinery operation:

EXAMPLE I The fluid catalytic cracker is charged with straight run distillate from the vacuum feed preparation unit which has the following characteristics:

' The conditions during catalytic cracking operation are as follows:

Reactor temperature, F. 950 Wt. hour space velocity 2.5 Catalyst/ oil ratio 2 8.1 Reactor pressure p.s.i.g 16.2 Slurry return B/ D r 216 Weight: of oil per hour/weight of catalyst in reactor bed.

1 Weight of catalyst circulated per hour/weight of oil feed per hour.

The yields from this catalytic cracking operation are as follows:

6. The heavy catalytic gas oil is then passed to the Dorr thickener wherein catalyst fines settle out and are removed for return to the catalytic cracker. The decanted slurry oil from the Dorr thickener is charged to a thermal cracking unit operating under the following conditions:

Rate, barrels/day 7,500

Temperature of furnace outlet F 940' The following yields are obtained:

Raw pressure distillate, vol. percent 1 20.5

Gas oil (410 F. to 700 F.), vol. percent 8.4

Heavy fuel oil to 150 SF. 122 F.),

vol. percent 65.8

3000 barrels of gas oil from the thermal cracking operation are treated with 3 vol. percent of 10 B. NaQH- after which 0.024 vol. percent of Santolene I-I inhibitor is added thereto. This is then blended with 7000 barrels of straight run diesel fuel from the atmospheric crude tower, having the following characteristics:

The finished automatic burner oil has the following analysis:

Gravity, API 30.9 Flash, F I 190 Pour, F 1 10 Viscosity, 8.11. at 100 F 37:0 Aniline point, F 138 Sulfur, perc 0.3'6

EXAMPLE II 4000 "barrels of gas oil from the thermal cracking operation and subsequent caustic and inhibition treatment as in Example I are blended with 6000 barrels of straight run diesel oil.

EXAMPLE III 5000 barrels of gas oil from the thermal cracking operation and subsequent caustic and inhibition treatment as in Example I are blended with 5000 barrels of straight run diesel oil.

EXAMPLE IV 2000 barrels of gas oil from the thermal cracking Dry gas, wt. percent 6.6 operation and subsequent caustic and inhibition treatment Propane cut, vol. percent 4.9 as in Example I are blended with 8000 barrels of straight Butane cut, vol. percent 10.3 55 run diesel oil. Lt. cat. naphtha, vol. percent 20.5 From the foregomg explanation and drawing coupled Heavy cat. naphtha, vol. percent 14.9 with an examination of appended Table I, the novelty Lt. cat. gas oil, vol. percent 9.1 and utility of the present invention will be clearly appreci- Med. cat. gas oil, vol. percent 18.5 ated. Resort may be had to such modifications and varia- Heavy cat. gas oil, vol. percent 20.3 0 tions as fall within the spirit of the invention and the C k t percent 5.7 6 scope of the appended claims.

Table I 100% 20% Cat. 30% Cat. Straight Product Product Product Product Cracked Gas Cracked Gas Run from Exfrom Exfrom Exfrom Ex- Oil 0ll+70% Diesel ample I ample II ample III ample IV DieseH-In- Diesel 011 hibitor Gravity. API a2. 6 3o. 9 32. 4 30. 2 30. 8 29. 6 29. 0 Flash, F 173 190 174 166 126 208 176 Pour, 15 +10 -10 --15 +10 +20 +15 Color, ASTM 336+ 3- 3 ,-s+ 3+ 4- 4% 8- Viscosit $.17. 39. 37.0 as. 0 36. 2 38.3 40.3 39. 2 Aniline oint,F..-.-

152 138 133 141 138 134 Sulfur, Wt. Percent 0. 39 0. 3e 0. a9 0.36 0. 57 0. 4s Bromine Number 7. 0 10. 2 10. 7 Sludge Formation (Accelerated Test) Good Good Good Good Good Very Poor Very Poor Table II.

100% Product Product Product Product 20% Cat. 30% Cat. Straight from from from 11'0111 Cracked Gas Cracked Gas Run Diesel Example Example Example Example Oll +80% 011 +70% Oll I II III I IV Dlesel+ Diesel Inhibitor Burner Tests: Stack Gas, Percent 11.0... 11. 11.0. 11." 11. 11. 11.0. Stack Temp.-

Start, F 445 440 440 405 430 400 445. End,F 520 525 480 50 510 57 595. Carbon Formed Light Medium Medlum. Medlum.. Medlum Heavy.- Heavy. Screen Deposits. N n N n N N n N n do Do. Burner Ratlng Very Good Goo Good Good Good Poor. Poor. Smoke Meter Start Good do do do do do Do. End (in do do do do j do Very Poor.

We claim: blended in the same proportions with gas oil prepared 1. The process for manufacturing a burner fuel which comprises: catalytically cracking a hydrocarbon distillate boiling above the gasoline boiling range, separating a fraction boiling above about 550 F. from the products formed, thermally cracking said fraction at a temperature between about 850 F. and 1000 F., separating a gas oil fraction boiling within the range of about 450 F. to 700 F. from the products of the thermal cracking step, and blending said gas oil fraction with a virgin gas oil boiling within said range in a ratio of one volume of said gas oil fraction to from 1 to 9 volumes of said virgin gas oil.

2. The process for manufacturing a burner fuel which comprises: catalytically cracking a hydrocarbon distillate boiling above the gasoline boiling range, separating a fraction boiling above about 550 F. from the products formed, thermally cracking said fraction at a temperature between about 850 F. and 1000" F., separating a gas oil fraction containing acidic bodies and boiling within the range of 450 F. to 700 F. from the products of the thermal cracking step, contacting said gas oil fraction with suflicient caustic to neutralize said acidic bodies, separating said gas oil fraction from said caustic, and then blending said gas oil fraction with a virgin gas oil boiling within said range in a ratio of one volume of said gas oil fraction to from 1 to 9 volumes of said virgin gas oil, said virgin gas oil having burning and storage characteristics which become unsatisfactory when blended in the same proportions with gas oil prepared by catalytically cracking virgin petroleum oil fractions and when by thermally cracking virgin petroleum oil fractions.

3. A burner oil made by catalytically cracking a hydrocarbon distillate boiling above the gasoline boiling range, separating a fraction boiling above about 550 F. from the products formed, thermally cracking said fraction at a temperature between about 850 F. and 1000" F., separating a gas oil fraction boiling within the range of about 450 F. to 700 F. from the products of the thermal cracking step, and blending said gas oil fraction with a virgin gas oil boiling within said range in a ratio of one volume of said gas oil fraction to from 1 to 9 volumes of said virgin gas oil.

4. A burner oil as in claim 3 which contains a minor amount, sufiicient to'improve the storage stability thereof, of a sludge inhibitor.

References Cited in the file of this patent Monsanto Chemical 00., Organic Chemicals Div., St. Louis 1, Mo.

Claims (1)

1. 3. A BURNER OIL MADE BY CATALYTICALLY CRACKING A HYDROCARBON DISTILLATE BOILING ABOVE THE GASOLINE BOILING RANGE, SEPARATING A FRACTION BOILING ABOVE ABOUT 550* F. FROM THE PRODUCTS FORMED, THERMALLY CRACKING SAID FRACTION AT A TEMPERATURE BETWEEN ABOUT 850* F. AND 1000* F., SEPARATING A GAS OIL FRACTION BOILING WITHIN THE RANGE

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