Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10F—DRYING OR WORKING-UP OF PEAT
  • C10F5/00—Drying or de-watering peat

Definitions

• Dewatering of peat can also be carried out by a process in which peat is disentangled by subjecting it to a breaking step, for instance in a conventional peat breaker.
• the disentangled peat is then slurried in water containing a flocculating agent and is then filtered.
• Filtration can be under pressure, for instance in a pressure filter for instance a belt press.
• a process according to the present invention for the removal of water from a wet material comprising combustible organic solid to form a solid autothermally combustible fuel comprises the steps of contacting the material with a dewatering liquid comprising a water-immiscible solvent and dissolved water-in-oil emulsifier and then extracting a water-in-oil emulsion from the mixture.
• the process of the invention is particularly suited for the dewatering of peat to render it sufficiently dry to be useful as a fuel, although it may also be useful for drying other wet organic solids to be subsequently used as fuels.
• the emulsion that is extracted from the mixture is cracked into a solvent layer and aqueous layer, and the solvent is recovered and recycled into the contacting step.
• Cracking of the emulsion may be carried out by known means, for instance by changing the pH, usually by acidifying the emulsion and also includes the addition of a common salt eg calcium chloride. Any debris which remains at the interfacial layer is in general discarded.
• the recycled solvent may contain some residual emulsifier, in general it is necessary to add more emulsifier to the solvent to form a satisfactory dewatering liquid.
• solvent since some solvent is discarded with the aqueous layer and interfacial layer, and some is retained in the product, it is necessary to continuously add solvent in the recycle process. Usually at least 50%, preferably at least 75% and more preferably more than 80%, for instance up to 90%, of the solvent is recycled. Sometimes it may be desirable to clean the solvent after use in several cycles to remove undesirable components dissolved in the solvent.
• the solvent may, for instance be distilled.
• the contacting step is generally in the form of slurrying, and is carried out in a vessel with stirring in order to ensure satisfactory mixing of the components.
• a suitable mixing device is a Heidolph stirrer, for instance used at a setting of 250 to 300 rpm.
• the mixer is fitted with a paddle stirrer to promote good contact of components, rather than intense shear.
• the time of mixing is sufficient to ensure good mixing and is preferably at least one or two minutes, and generally does not need to be more than about 60 minutes, usually less than 30 minutes, for instance 5 to 20 minutes. Were the resultant slurry subjected to a higher rate of stirring or shear, then the time may be less. It is in general found that it is not advantageous, or is even disadvantageous, to prolong the shearing period or to increase the intensity of mixing beyond the minimum required for good contact of the components.
• the extraction of the emulsion from the mixture is in general carried out by the processes of the type used for dewatering aqueous flocculated peat slurries.
• the extraction thus generally includes filtration, preferably pressure filtration, for instance on a belt press.
• the material is suitably subjected to a pressure of at least 5 bar, preferably at least 10 bar for instance about 15 bar.
• the wet material which is usually peat, which is subjected to the defined steps of the present invention, has preferably already been subjected to a preliminary drying step or a plurality of such steps.
• peat may be subjected to the conventional slurrying in water containing a flocculant followed by pressure filtration.
• the process of the invention also covers processes including such a preliminary step.
• the peat may be dried in a preliminary step by contact with absorbent materials, capable of absorbing the moisture. Such materials are subsequently removed from the peat.
• absorbent materials capable of absorbing the moisture.
• suitable materials are for instance water-swellable insoluble polymer particles.
• Suitable polymers are described in GB 1,573,201 and, are preferably of the type described in EP-A-0,195,550. Such polymer particles are for instance used by mixing disentangled peat with polymer particles and then separating the swollen polymer by sieving the mixture.
• the material that has had the emulsion extracted may be subjected to a subsequent further drying step, or other treatment step, for instance to remove further solvent if desired.
• Such further steps include evaporation of water and/or solvent eg by heating.
• the peat, or other wet material generally has a water content of less than 90%, preferably less than 80%, more preferably less than 70% by weight prior to the step of slurrying in the dewatering liquid.
• the moisture content of the material after extraction of the water-in-oil emulsion is less than 80%, preferably less than 70%, and more preferably less than 60%.
• the amount of water which is removed from the wet material by the dewatering liquid at least 10%, preferably at least 20%, and even up to 25, 30 or more % of the total water present in the material before the contacting step.
• the amount of solvent remaining in the fuel is preferably less than 20% by weight, more preferably less than 15% by weight.
• Solvents which are useful in the present invention are hydrocarbon solvents, generally petroleum solvents or other non polar solvents.
• the solvents should have as low a volatility as possible to minimise problems with handling the dried material.
• the solvent should have a low viscosity in order to improve the amount of emulsion which can be extracted from the product and to give easier handling of the mixture during the process.
• Preferred solvents are kerosenes. Kerosenes consist of petroleum hydrocarbons having about 10 to 60 carbon atoms per molecule. Examples of preferred kerosenes include Exxol D240/270, Solvent 41 and SBP11.
• the emulsifier can be any water-in-oil emulsifier which is soluble in the solvent and which is capable of forming an emulsion in the contacting process.
• Suitable emulsifiers are nonionic surface active agents, for instance fatty acid esters.
• Preferred emulsifiers include nonyl phenol-ethylene oxide condensate (Span 80) and sorbitan mono-oleate (Montane 80).
• the emulsifier is used in the dewatering liquid in a sufficient amount for emulsification of the water. The amount should be at least 0.1%, preferably at least 0.5% (by weight) based on the amount of solvent plus emulsifier. In general it is unnecessary to add more than around 10, or even more than 5%.
• the dewatering liquid can contain other components in addition to the solvent and emulsifier.
• Such additives may be for altering the viscosity of the liquid and/or emulsion or for adding formation or cracking of the emulsion.
• the liquid may even include water and may therefore be an emulsion itself, such emulsions have been found to act as dewatering liquids.
• the dewatering liquid is generally added to the wet material to give a ratio of wet material:liquid in the range of 1:1 to 1:10 (weight/kg:volume/l), preferably 1:2 to 1:5.
• An alternative method of contacting, other than by slurrying, is by spraying the wet material with the dewatering liquid.
• the solvent is allowed to drain through the wet material, which is then pressed to remove water and excess solvent.
• Solvent can be recovered from the process by acid cracking, as described earlier, and can be re-cycled.
• the process can be carried out on either small scale or large scale.
• An alternative large scale route would be a batch conditioning system.
• the filtrate from the first sample was hazy pale yellow in colour and contained a few droplets of water.
• the dry solids of the combined products was found to be 28.16%.
• a 50 g. sample of the dewatered peat was slurried in 200 cm3 of a mixture of solvent (SBP11) containing 5% Span 80 emulsifier. The slurry was mixed on the Heidolph stirrer at setting 0 for 5 minutes before pressing on the lab. piston press at 15 bar. The composition of the final product was:- TABLE 5 DS Water Kerosene Percentage Compn. 37.12 48.0 14.88 Wt Ratio Compn 1 1.29 0.40
• Example 6 The technique can be applied to sewage sludge and other organic slurries, as illustrated in Example 6 below:

Landscapes

• Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Organic Chemistry (AREA)
• Treatment Of Sludge (AREA)
• Polymerisation Methods In General (AREA)
• Liquid Carbonaceous Fuels (AREA)
• Solid Fuels And Fuel-Associated Substances (AREA)

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Citations (5)

• 1989
  • 1989-02-13 GB GB898903172A patent/GB8903172D0/en active Pending
• 1990
  • 1990-02-08 DE DE1990601620 patent/DE69001620T2/de not_active Expired - Fee Related
  • 1990-02-08 EP EP19900301333 patent/EP0383485B1/fr not_active Revoked
  • 1990-02-12 CA CA 2009797 patent/CA2009797A1/fr not_active Abandoned
  • 1990-02-12 IE IE49890A patent/IE900498L/xx unknown
  • 1990-02-12 FI FI900680A patent/FI900680A0/fi not_active IP Right Cessation
  • 1990-02-12 NO NO90900665A patent/NO900665L/no unknown
  • 1990-02-13 NZ NZ23252090A patent/NZ232520A/en unknown

Patent Citations (5)

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