GB2330150A

GB2330150A - Process for the agglomeration of petroleum coke fines

Info

Publication number: GB2330150A
Application number: GB9721596A
Authority: GB
Inventors: Trevor H Andrew; Peter Lees
Original assignee: APPLIED IND MATERIALS UK Ltd
Current assignee: APPLIED IND MATERIALS UK Ltd
Priority date: 1997-10-13
Filing date: 1997-10-13
Publication date: 1999-04-14
Anticipated expiration: 2017-10-13
Also published as: GB2330150B; GB9721596D0

Abstract

A particulate composition comprising particulate petroleum coke and a particulate non-combustible material in an amount of from 1 to 10% by weight based on the weight of the particulate petroleum coke is agglomerated to form a particulate solid fuel by mixing with a phenol-formaldehyde resole resin in alkaline aqueous solution, as binder, and one or more organic esters selected from esters of polyhydric alcohols, carbonate esters and lactones, as curing agent for the phenolic resin binder, forming the mixture into agglomerates and allowing the resin binder to undergo cure by reaction with the curing agent. The resulting agglomerate, which contains no coal-based fuel, has use as a domestic solid fuel.

Description

PROCESS FOR THE AGGLOMERATION OF PETROLEUM COKE FINES The present invention relates to a process for the agglomeration of petroleum coke fines. Petroleum coke is the solid material that is produced when the bottom-of-the-barrel material, at an oil refinery, is heated at a sufficient temperature and for a sufficient period of time to drive off more volatile components, leaving a solid residue.

It is composed mainly of carbon and typically contains around 10% by weight of volatile hydrocarbon materials and, in addition, trace metals and sulphur. The petroleum coke is usually formed in a batch coking process in drums. After a drum is filled with coke, water cooled and drained it is opened and the coke is cut out hydraulically with high pressure water. The coke cutting process produces large chunks of coke through to fines (particulate coke).

Other methods of production can use a continuous fluidised bed process that produces a finer type of petroleum coke, with less volatile matter.

A variety of methods are known for producing fuel briquettes from agglomerations of coal fines and often these involve the use of binders such as sulphite lye, urea-formaldehyde resin, phenolformaldehyde resin1 polyvinyl alcohol or bitumen.

However, the known processes for producing briquettes from coal fines have disadvantages. The level of ash in the finished product is determined by the ash content of the components. It is therefore not possible to control the desired level of ash in the final product without changing the feed stock. It is often not possible to obtain suitable feed stocks which have both the desired properties for agglomeration and a suitable ash content. Furthermore, the precise levels of ash in the various blend components are difficult to quantify during the production process and indeed can vary throughout the feed stock, so leading to inaccuracy in the ash level in the final product.

Petroleum coke, on its own however, does not have sufficient ash present to be regarded as a satisfactory fuel for use in domestic heating appliances because of the risk of overheating of the grate or lower firebox due to the lack of sufficient ash present in the fire zone.

The aim of the present invention is to provide a process whereby fuel briquettes or agglomerates of various shapes and sizes for use in domestic heating appliances can be produced using petroleum coke as the sole fuel component. Accordingly, the present invention provides a process for the agglomeration of a particulate solid fuel comprising forming a mixture of the particulate solid fuel, a phenol-formaldehyde resole resin in alkaline aqueous solution as binder therefor and, as curing agent for the resole resin binder, one or more organic esters selected from esters of polyhydric alcohols, carbonate esters and lactones, forming the mixture into agglomerates and allowing the resole resin binder to undergo cure by reaction with the curing agent characterised in that the particulate solid fuel comprises particulate petroleum coke and in that the mixture also comprises a particulate non-combustible material in an amount of from 1 to 10% by weight based on the weight of the petroleum coke and in that the mixture contains no coal-based fuel.

We have found that by blending the particulate petroleum coke with a particulate non-combustible material and by binding the mixture with an ester-curable alkaline phenol-formaldehyde resole resin and then curing the ester-curable resole resin by reaction with the organic ester an agglomerate is obtained which is suitable for use as domestic fuel.

The phenol component of the phenol-formaldehyde resole resin will usually be phenol itself although it is within the scope of the invention to use other monohydric phenols, such as cresol. or dihydric phenols, such as resorcinol, and mixtures thereof as the phenol component. The phenol-formaldehyde resole resin will typically be prepared by reacting together the phenol and formaldehyde in the presence of an alkali such as sodium hydroxide or potassium hydroxide. The molar ratio of phenol to formaldehyde will usually be in the range of from 1:1 to 1:3. The alkaline aqueous solution of the resole resin may have additional alkali added to it, before being mixed with the other components of the precure mixture, if desired. The actual concentration of alkali in the mixture will be chosen depending on the desired setting or hardening time of the agglomerates, on the required ultimate strength of the final agglomerates and on the actual composition of the resole resin used. Typically, the total alkali content will be in the range from 4 to 20% by weight based on the weight of the resin solution or from 20 to 40% by weight based on the weight of the resin itself.

The resole resin is cured by reaction with one or more organic ester curing agents selected from esters of polyhydric alcohols, carbonate esters and lactones. Typical esters of polyhydric alcohols are those formed by the reaction of a polyhydric alcohol, such as ethylene glycol, propylene glycol and glycerine, with formic acid or a lower (1-6C) alkyl carboxylic acid, such as acetic acid. A preferred ester for use in the present invention is triacetin (glycerine triacetate).

Typical organic carbonate esters include, as an example, propylene carbonate. Lactones that can be used as ester curing agents include gamma-butyrolactone, caprolactone and propriolactone.

The quantity of alkaline phenol-formaldehyde resole resin solution used in the mixture will usually be in the range of from 3 to 8% by weight based on the weight of the petroleum coke fines and the quantity of the ester curing agent will usually be from 5 to 20% by weight based on the weight of the resin solution.

The agglomerate mixture contains non-combustible material in an amount of from 1 to 10% by weight based on the weight of the petroleum coke fines. The non-combustible material is a material which does not act as a fuel component but has the function, when the agglomerate is burned, as an insulator to prevent overheating of the grate or lower firebox due to the lack of ash in the fire zone.

The non-combustible material also acts as a smothering agent for burning particles of petroleum coke which may fall through the grate bars in a domestic appliance into the ash pan. Examples of suitable non-combustible materials include pulverised fly ash, clay and calcium carbonate, such as limestone. The use of limestone, as the non-combustible material, in the production of the agglomerate gives rise to an additional advantage in that it helps to reduce the sulphur level of the chimney emissions produced on combustion of the agglomerate. We believe this effect results from a chemical bonding occuring between the calcium content of the limestone and the sulphur contained in the petroleum coke, during combustion of the aggregate, which leaves less sulphurous combustion gases to be vented to the atmosphere. The amount of non-combustible material used in the agglomerate is determined from the ash level of the petroleum coke fines (typically 0.5% by weight) and from that required in the finished briquettes.

Preferably, the amount will be such to provide a content of noncombustible material of from 3 to 5% by weight based on the weight of the finished briquette.

According to a preferred embodiment, the agglomerate will also contain a green-strength enhancer to improve the green-strength of the mixture prior to the hardening of the binder caused by the reaction of the resole resin with the ester curing agent. We have found that polysaccharides are particularly suitable green-strength enhancers. Examples of suitable polysaccharides include natural gums, such as guar gum. The quantity of the green-strength enhancer used will depend on the severity of handling which the agglomerates are expected to suffer prior to the resin binder developing sufficient strength. Typically, when guar gum is used as the green-strength enhancer it will be incorporated into the mixture in an amount of about 0.5% by weight based on the weight of the petroleum coke fines. Preferably, the guar gum is one specified as having 100% passing through a 200 mesh Tyler Standard Screen 1910, with a viscosity of 3,500 cps (1% aqueous solution after 24 hours cold water hydration at 1 80C).

The resulting mixture may then be formed into agglomerates, such as briquettes, by any of the means commonly used to produce coal briquettes.

The preferred method of producing the agglomerates is to compact the mixture in moulds, under pressure using a roll press, preferably having a plurality of moulds.

The agglomerates will usually begin to cure immediately, with the resin bonding system developing strength during 10-60 minutes at ambient temperatures, sufficient for the briquettes to be handled by conventional means. If a green-strength enhancer is incorporated into the mixture the agglomerates have enhanced initial strength, particularly when produced in a roll press. Lower ambient temperatures result in a slower curing time.

Full strength develops at ambient temperature over a period of 1-1 5 days, depending on the prevailing temperature, and needs no additional drying or heating to produce the full curing process of the resin binder.

EXAMPLE An alkaline phenol-formaldehyde resole resin was prepared by blending 26 parts by weight of an aqueous sodium hydroxide solution containing 50% by weight of sodium hydroxide and 74 parts by weight of an aqueous phenol-formaldehyde resin having a phenol to formaldehyde molar ratio of 1:1.7.

Petroleum coke containing 7.5% by weight moisture and 0.5% by weight ash was mixed with 4% by weight limestone and crushed in a roll crusher set at 2mm opening to produce a fines mixture.

0.5% by weight guar gum powder was added, 5% aqueous resin (based on the weight of the petroleum coke fines) and 0.75% triacetin (based on the weight of the petroleum coke fines) were mixed and added to the solids mixture along with a further 3% (by weight of petroleum coke fines) water. The mixture was stirred to ensure a homogenous blend.

The resulting mixture was then immediately formed into 30 c.c. briquettes through roll press moulds set at 2.5 tonne linear pressure (200 bar).

After allowing 5 days for curing at the prevailing ambient temperature (1 50C) the briquettes produced had good surface hardness, were water resistant and had a compression strength of 80kgs.

Claims

CLAIMS 1. A process for the agglomeration of a particulate solid fuel comprising forming a mixture of the particulate solid fuel, a phenol-formaldehyde resole resin in alkaline aqueous solution as binder therefor and, as curing agent for the resole resin binder, one or more organic esters selected from esters of polyhydric alcohols, carbonate esters and lactones, forming the mixture into agglomerates and allowing the resole resin binder to undergo cure by reaction with the curing agent characterised in that the particulate solid fuel comprises particulate petroleum coke and in that the mixture also comprises a particulate non-combustible material in an amount of from 1 to 10% by weight based on the weight of the particulate petroleum coke and in that the mixture contains no coal-based fuel.
2. A process according to claim 1, wherein the particulate non combustible material is selected from pulverised fly ash, clays , limestone and mixtures thereof.
3. A process according to either claim 1 or claim 2, wherein the particulate non-combustible material is added to provide a content in the agglomerate in the range from 3 to 5% by weight based on the weight of the finished agglomerate.
4. A process according to any one of claims 1 to 3, wherein a green-strength enhancer is present in the mixture
5. A process according to claim 4, wherein the green-strength enhancer is guar gum used in amount of about 0.5% by weight based on the weight of particulate petroleum coke.
6. A process according to any of the claims 1 to 5, wherein the phenol-formaldehyde resole resin has a molar ratio of phenol to formaldehyde of from 1:1 to 1:3.
7. A process according to any of claims 1 to 6, wherein the amount of alkali present is 4-20% by weight based on the weight of phenol-formaldehyde resin solution.
8. A process according to any of claims 1 to 7, wherein the curing agent is triacetin.
9. A process according to any of claims 1 to 8, wherein the quantity of alkaline phenol-formaldehyde resole resin solution used is 3-8% by weight based on the weight of the particulate petroleum coke and the quantity of curing agent is 5-20% by weight based on the weight of the resin solution.
10. A process according to anyone of claims 1 to 9, wherein the agglomerates are formed by compacting the mixture by pressing or pelletising or other means of forming into briquettes or pellets.