Patent Application
20140024879
The present invention relates generally to a combustible fuel for cement kilns. The present invention further relates to a combustible fuel that comprises a blend of oil refinery sludge and glycerin byproducts. The present invention also relates to a method of producing a useful fuel product from refinery sludge wastes and glycerin byproducts.
Refinery sludge wastes, including those from centrifuges and thermal desorption units (TDU) typically contain solids, moisture and oil. A typical refinery centrifuge cake would have 40% solids, 52% moisture content and 8% oil content. A typical TDU powder would have 80% to 83% solids, 6% to 8% moisture and 8% to 13% oil content. When a TDU is coupled with a centrifuge in a refinery waste water treatment plant, it can typically cut the quantity of centrifuge cake requiring expensive offsite disposal in half. Refinery centrifuge cake and TDU powder solids have to be handled in rolloff boxes that must either be disposed as listed hazardous wastes at a hazardous waste incinerator or at a select few cement kilns that have the capability to receive non-pumpable solids.
Back 15 to 20 years ago, when the EPA RCRA Land Ban Restrictions (LDR) regulations first went into effect, it was known to blend refinery centrifuge cake, filter press cake and/or TDU powder approximately 50:50 with either used motor oil or with refinery Cat Cracker Unit (CCU) slurry oil. The mixture was shipped in agitated “RobeRoller” tankers as a liquid fuel to cement kilns.
All cement kilns that are permitted to burn hazardous waste fuels are capable of receiving such blended liquid fuels so long as they are pumpable. While it is known to ship non-pumpable sludges in rolloff boxes to RCRA incinerators or solids-handling cement kilns, the pricing for the pumpable blended liquid fuels are typically only $60 to $80 per ton, compared to $350 to $450 per ton for the non-pumpable sludges. Since the price of used motor oils and CCU oils have gone up significantly, used motor oil and/or CCU oil sludge blending as a fuel for cement kilns is no longer economical.
The production of biodiesel via transesterification of vegetable oils, animal oil/fats, tallow and waste oils produces glycerin as a by- or coproduct. Glycerin is a highly viscous liquid due to its three hydroxyl groups which interact between molecules via hydrogen bonding. Glycerin is typically too viscous at ambient temperature to be used as a fuel. In addition, glycerin has a high melting point and decomposes during distillation. Glycerin has a limited market in some products like explosives (nitroglycerine), cosmetics, and lubricants. In some markets, the only outlet for glycerin byproducts is for use in animal feed. The volume of glycerin that will be produced as biofuels grow in production will be in great excess of these limited markets. It is estimated that the supply of glycerin from the biodiesel industry will continue to dwarf demand until more than 5 billion pounds are expected to hit the world by 2020.
The present invention provides a method of producing a useful fuel product from refinery sludge wastes and glycerin byproducts.
According to various features, characteristics and embodiments of the present invention which will become apparent as the description thereof proceeds, the present invention provides a combustible fuel composition which comprises a blend of:
refinery sludge; and
glycerin,
wherein the glycerin comprises about 20-80 weight percent of the blend.
The glycerin can comprise a purified glycerin or a glycerin byproduct from a biodiesel process that may include other components such as methanol, water and solids. Reference herein to “glycerin” encompasses both purified glycerin and glycerin byproduct unless otherwise indicated. In this regard it can be readily understood that a blend of refinery sludge and purified glycerin according to the present invention would be a suitable fuel even though according to the present invention it is not necessary to use purified glycerin in place of glycerin byproducts.
The refinery sludge can comprise centrifuge filter cake, filter press cake, belt press cake, tank bottom sludge, thermal desorption unit powder or combinations thereof.
While the glycerin can broadly comprises 20-80 weight percent of the blend, according to one embodiment the glycerin can comprise about 50-60 weight percent of the blend.
The present invention further provides a method of producing a combustible fuel composition, which method comprises:
providing a refinery sludge;
providing glycerin; and
combining the refinery sludge and glycerin to form a blend.
Depending on the nature of the refinery sludge (if it contains any chunks or large solids), it may be necessary to use a premix tank, a high speed disperser mixer or an attritor to perform the initial blending of the sludge with the glycerin.
During the course of the present invention it was unexpectedly discovered that if the glycerin byproduct started out as a vaseline like solid at ambient temperature, in many cases after it was heated and blended with the refinery sludge, it turned into a pumpable liquid that remained pumpable at ambient temperature.
In further embodiments moisture and any methanol and light hydrocarbons are removed after refinery sludge and glycerin are combined to form the blend.
The moisture and any methanol and light hydrocarbons can be removed by heating the blend in a vessel or by processing the blend in a flash evaporator.
In the method the glycerin can comprise a purified glycerin or a glycerin byproduct from a biodiesel process that may include other components such as methanol, water and solids.
In the method the refinery sludge can comprise a centrifuge filter cake, filter press cake, belt press cake, tank bottom sludge, thermal desorption unit powder or combinations thereof.
In the method the refinery sludge can comprise centrifuge cake that is obtained heated from a centrifuge and the glycerin can be preheated before being blended with the refinery sludge.
The refinery sludge and glycerin can be combined in a proportion so that the glycerin comprises about 20-80 weight percent of the blend depending on the solids and oil content of the refinery sludge. Accordingly to another embodiment the refinery sludge and glycerin can be combined in a proportion so that the glycerin comprises about 50-60 weight percent of the blend.
The present invention further provides a method of disposing of refinery sludge, which method comprises:
providing a refinery sludge;
providing glycerin;
combining the refinery sludge and glycerin to form a blend; and
burning the blend in a cement kiln.
In the method the glycerin can comprise a purified glycerin or a glycerin byproduct from a biodiesel process that may include other components such as methanol, water and solids.
In the method the refinery sludge can comprise a centrifuge filter cake and/or thermal desorption unit powder.
According to one embodiment of the method before the blend is burned in a cement kiln, moisture from the blend together with any methanol and light hydrocarbons originally present in the blend are removed.
Such moisture can be removed by processing the blend in a flash evaporator or heating the blend in a vessel.
The present invention also provides a method of processing glycerin byproducts from biodiesel production processes which method comprises:
combining the glycerin with refinery sludge to form a glycerin sludge blend; and
burning the glycerin sludge blend.
In the method the refinery sludge can comprise a centrifuge filter cake, filter press cake, belt press cake, tank bottom sludge, thermal desorption unit powder or combinations thereof.
According to one embodiment of the method moisture from the blend together with any methanol and light hydrocarbons originally present in the blend are removed.
The present invention will be described with reference to the attached drawings which are given as non-limiting examples only, in which:
The present invention is directed to a combustible fuel that comprises a blend of refinery sludge and glycerin or glycerin byproducts. The present invention further is directed to a method of producing a useful fuel product from refinery sludge wastes and glycerin or glycerin byproducts, thereby meets the need to recycle refinery sludge wastes while providing a practical use for the current glut of glycerin, including glycerin byproducts. The glycerin refinery sludge blend can be used as a primary or auxiliary fuel in a cement kiln.
In general the glycerin sludge blend is prepared by combining the refinery sludge with glycerin. The glycerin can be preheated before being combined with the refinery sludge. The centrifuge cake is typically already warm from the centrifuge processing. According to one embodiment moisture can be removed from the mixture by flash evaporator or heating the mixture in a vessel.
During the course of the present invention it was determined that when glycerin byproducts, which have a vaseline or thick cream-like consistency at room temperature, are heated to 120-130° F. they are easily pumpable.
When mixed with refinery sludge it was discovered that some glycerin samples would gel up and get very thick or solidify, thus defeating the goal of developing a flowable and pumpable glycerin sludge blend mixture.
In order to qualify which glycerin samples were able to produce a flowable and pumpable glycerin sludge blend mixture glycerin samples from seventeen sources were mixed with the same amounts of the same sludge solids sample and subjected to mixing that simulated the mixing intensity (mixer tip speed) in a Baker mix tank for 24 hours at ambient lab temperature. The measured viscosities of the resulting glycerin sludge blend mixtures varied from over 40,000 centipoise to less than 5,000 centipoise. Over this range it was determined that a viscosity of about 8,000 centipoise or less provided glycerin sludge blends that were suitably flowable and pumpable for purposes of the present invention.
In order to characterize which types of glycerins would produce flowable and pumpable glycerin sludge blends the glycerin samples used above were subjected to Fourier Transform Infrared Spectroscopy and the ratio of the hydroxide concentration to the aliphatic hydrocarbon content of the glycerin samples (referred herein as the FTIR ratio”) were plotted against the viscosities of the sample blends. The FTIR ratios varied from about 0.1 to 3.5 and it was determined that in order to produce a glycerin sludge blend having a viscosity of about 8,000 centipoise or less a glycerin having a FTIR ratio of about 1.45 or higher should be used.
Tests conducted during the course of the present invention showed that in general samples of glycerin byproduct from different biodiesel facilities had from about 6,000 to about 10,700 BTU/lb. Since the EPA has established that a waste product fuel has to have a BTU value of at least 5,000 in order to be classified as a “fuel” for use in combustion furnaces, glycerin can be considered a fuel; however, attempts to burn glycerin itself as a fuel have had limited success at best. The present invention is directed to a glycerin sludge blend which can burn in conventional cement kiln furnaces as a primary or auxiliary fuel.
The glycerin and refinery sludge can be blended at a ratio of 20-80 weight percent of glycerin to 20-80 weight percent of refinery sludge and preferably 50-60 weight percent of glycerin to 50-40 weight percent refinery sludge. The amount of refinery sludge used in the blend is limited when the amount no longer produces a pumpable fuel blend.
According to one embodiment of the present invention a heated sealed mixing tank can be used and configured so that a centrifuge cake conveyor can discharge directly into it. The tank would be heated sufficiently to provide heat if the sludge feed was cold and/or to keep the mixture warm and easily pumpable. The glycerin could be metered into the tank to match the centrifuge cake or sludge conveyor feed rate. In this embodiment the process could operate in a continuous, semi-continuous or batch manner.
The heated sealed mixing tank can be sized to approximately 6,700 gallons so as to hold about 33 tons of glycerin sludge blend. This would equate to about 1.5 truckloads. When it was time to transfer the glycerin sludge blend to an insulated tanker for shipment to a cement kiln one truckload (about 22 ton) of the glycerin sludge blend could be removed, leaving an 11 ton heel in the tank of 1.5 feet so that glycerin and cake feed could continue during truck loading. A larger 17,000 gallon to 20,000 gallon mix tank could be used for sludge blending and storage for larger projects.
According to another embodiment of the present invention refinery sludge and glycerin are combined in a high speed disperser or attritor. In this embodiment a centrifuge cake conveyor or a separate sludge conveyor can be setup to handle filter press cake, belt press cake or tank bottoms sludges and feed them into premix tank in which the glycerin and sludge is preliminarily blended and then into a high speed dispenser or attritor. The high speed disperser or attritor will produce a glycerin sludge blend in which particle sizes of components of the sludge will be reduced to ensure suspension. The resulting glycerin sludge blend can be pumped to a glycerin sludge blend storage tank for shipment to a cement kiln.
According to another embodiment of the present invention centrifuge sludge cake and glycerin are combined in a mixing tank. The centrifuge sludge cake can be fed into the mixing tank directly from the centrifuge via a centrifuge cake conveyor so to retain heat and be preheated. The glycerin can stored in a heated tank and thereby can be preheated as it is fed into the mixing tank.
In this embodiment the glycerin sludge blend is fed from the mixing tank through a flash evaporator which causes steam, methanol and light hydrocarbons to flash off and exit as hot vapor. The remaining glycerin sludge blend is recovered as a fuel product for cement kilns.
The mixing of the sludge filter cake and glycerin produces a glycerin sludge blend that is transported to a heat exchanger 30 via line 29 as depicted. Heat exchanger 30 uses steam or hot oil to heat the incoming glycerin sludge blend to a suitable temperature, e.g. 230° F. at which the steam, methanol and light hydrocarbons can be removed in the flash evaporator 31. The heated glycerin sludge blend is fed into the flash evaporator 31 at an elevated pressure of for example at least 5 psi and preferably 15-20 psi or greater. The flash evaporator 31 is provided with a regulated back-pressure valve through which the heated glycerin sludge blend is passed therethrough and into a flash evaporator tank so that the steam, methanol and light hydrocarbons are released and removed as hot vapors in line 26 and sent to a vapor collecting, condensing and processing system 27. The glycerin sludge blend product is recovered in line 28 and can be stored in a product mix tank or shipped in an insulated tanker to a cement kiln.
In the cement kilns, the glycerin sludge blend is injected into the combustion zone. It is noted that as regards burning blends of refinery sludge and glycerin cement kilns are an attractive way of disposing of these materials, as opposed to incineration because the cement kilns use of the heat to produce a product offers lower disposal costs verses incinerators, and because the alkaline conditions in cement kilns, afforded by the high-calcium raw mix, can absorb acidic combustion products, and because of the ability of the clinker to absorb heavy metals into its structure.
Although the present invention has been described with reference to particular means, materials and embodiments, from the foregoing description, one skilled in the art can easily ascertain the essential characteristics of the present invention and various changes and modifications can be made to adapt the various uses and characteristics without departing from the spirit and scope of the present invention as described above and set forth in the attached claims.
This application is based on U.S. Provisional Application Ser. No. 61/673,367, filed Jul. 19, 2012 to which priority is claimed under 35 U.S.C. §120 and of which the entire specification is hereby expressly incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61673367 | Jul 2012 | US |
