Furnaces – Process – Supplying fluid
Patent
1995-04-07
1997-08-12
Bennett, Henry A.
Furnaces
Process
Supplying fluid
110224, 110306, 34413, F23L 100
Patent
active
056554664
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method for feeding a water-containing fuel such as peat or brown coal into a pressurized space.
The method also concerns a configuration for implementing the method.
DESCRIPTION OF THE BACKGROUND ART
The feed of solid material into a pressurized dryer, high-pressure gasifier or any other similar pressurized space is complicated. The greatest difficulties in fuel feed are met when the material to be fed must be transferred over a pressure differential to a higher pressure. The easiest approach would be to feed the fuel by pumping, whereby pressure elevation and transfer of the fuel mixture to a higher pressure could be managed by means of a relatively simple pump without resorting to high-cost special arrangements. The mixture to be pumped must in this case, however, be at a sufficiently high moisture content to permit its transfer by a pump or a ram feeder. If the moisture content of the mixture falls below a material-specific pumpability limit, expensive special methods must be employed for fuel feed. When the moisture content alternatively is elevated to the pumpability limit, the input power to the dryer units employed in the system must be increased, which may result in lower energy generation efficiency of the process and cause unprofitable operation of the system. Therefore, economical gain would be attained through a method capable of feeding water-containing fuels by pumping in an advantageous manner and yet maintaining the profitable and functional capabilities of the system.
In terms of peat production, transport and the process discussed above, the optimal moisture content of peat has been estimated at 60-70%. The pumpability limit of peat is, however, slightly higher than this with a lower limit of at least 75%, while as high figures as 90% and above for pumpability are quoted in the literature of the art. In the tests performed by the applicant, the pumpability limit has typically been in the range of 72-73%, while feeding peat with approx. 65% moisture content has been successfully carried out. These figures indicate that the pumpability limit in terms of process and fuel production factors lies close to the upper limit of the fuel moisture content range. Thus, the fuel is advantageously moisturized for easier feed prior to its feed into the pressurized space.
The Finnish patent application 894,588 discloses a method in which slurried fuel with a high moisture content is fed by pumping into a high-pressure space. In this space the slurry is next dewatered by mechanically removing a sufficient amount of water until the fuel can be fed either directly into a boiler, or alternatively, via a dryer into a high-pressure gasifier. Drying the fuel takes place by, for instance, filtering the water away from the fuel through a permeable wall from the high-pressure space to the ambient pressure. Fuel dewatered in this manner can be combusted in a fluidized-bed boiler without any need for additional drying. If the fuel is gasified, additional drying with the help of a steam dryer must be applied.
The above-described method results in complicated equipment arrangement. Equipment located in the pressurized space is subject to constructional special requirements and the arrangement for filtrate removal over the pressure differential without pressure loss is difficult. This method provides no essential benefit in the gasification of the fuel as the fuel must in any case be subjected to further drying in a pressurized dryer, whereby mechanical drying at elevated pressure solely complicates the equipment layout. Mechanical drying at elevated pressure in conjunction with gasification is justified only when the moisture content of the fuel used is so high as not to permit economical drying in a pressurized dryer.
Further, the Finnish patent 86,219 discloses a method in which coal used as a fuel is moisturized with hot water or steam generated with the waste heat of boiler ash. After increasing the moisture content of the fuel, it can be fed by pu
REFERENCES:
patent: 3654705 (1972-04-01), Smith et al.
patent: 3815522 (1974-06-01), Larger
patent: 3992784 (1976-11-01), Verschuur et al.
patent: 4422246 (1983-12-01), Hardesty et al.
patent: 4742623 (1988-05-01), Meurer et al.
patent: 4949655 (1990-08-01), Greer et al.
Aijala Martti
Hulkkonen Seppo
Bennett Henry A.
Imatran Voima Oy
Tinker Susanne C.
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