Objective
The continuous pressure filter type KDF has been developed for the dewatering of large throughputs of solids as, for instance, has to be done in applications such as coal and mineral preparation and cement production. In all these applications conventional mechanical dewatering still yields a product with such a moisture content that additional thermal drying is needed, with consequently very high costs due to the enormous energy consumption. Depending on the products, the KDF eliminates this thermal drying or it can be done with a significantly lower energy consumption.
1. Comparison of the actual situation at customer's site to the past one
In the past it was needed to dry the total coal/ash production as a mixture (50/50) (hundred tonnes an hour) with approximative 35 % end humidity after the "old" filter presses. Now, i.e. with the KDF, only 50 tonnes of coal per hour, with an approximative end humidity of 19 % water has to be dried, if necessary at all. The former process with its end humidity of 35 % in that fraction of the production, made thermal drying necessary. With the KDF's the production with 18 - 20 % end humidity can be mixed in the rest of the production, without thermal drying afterwards. So to obtain 100 tonnes bone dry coal/ash mixture 153 tonnes (with a humidity of 35 %) of total product has to evaporate 53 tonnes of water. The end product contained still 50 % ash. On the other hand these 100 tonnes per hour coal/ash mixture is not marketable anymore due to environmental reasons. In the present process 50 tonnes bone dry coal(ash only being 10 - 12 %) are obtained by separating the first coal/ash mixture in the flotation and filtering of the coal only to a humidity of 19 %. So to obtain the same caloric value (50 tonnes bone dry coal) only 62 tonnes mixture has to evaporate 12 tonnes of water. The difference is thus 53 - 12 = 41 tonnes of water per hour to be evaporated.
2. Comparison of the use of conventional filters to KDF
Because no industrial conventional filters are used at the customer's site we have to base ourselves on the tests on lab-scale done with such conventional filters. They yielded a moisture content of over 30 % with vacuum filtration. The total investment (equipment and building) will go over the investments of the KDF-installation, still yielding a product with a 11% higher moisture content (30 - 19 %).
For the evaluation in Belgium we will neglect the difference in investments for reasons mentioned above. Also we will neglect the difference in direct energy consumption of the installation, although this is expected to be lower.
Energy savings :
Base :
- 50 t/h 5000 h/year (bone dry coal);
- difference between vacuum filtration and KDF over 11 %;
- efficiency thermal drying approx. 70 %.
3. Energy savings
Conventional vacuum filtration yields a product of 50 tonnes bone dry coal with 21,4 tonnes water (30% out of 71,1 tonnes filter cake). The KDF-installation yields 50 tonnes bone dry coal with 11,7 tonnes water (19% out of 61,7 tonnes filter cake).
Shortly summarized : the energy savings per year is 3.740 TOE.
In spite of the situation in the coal industry we therefore sold recently the licence of the KDF for Japan and Australia to the japanese company Tomoe Engineering Co. LTD.
Pressure filtration as well as continuous filtration are common operations. However, the combination, although often tried, has never been successful and certainly not for high solid throughputs. Due to the difficulties encountered to get the dewatered solids out of the pressure vessel, conventional pressure filtration is always a discontinuous process, the more so when high solid concentrations or big quantities are involved. This makes the system not acceptable for the potential markets of the KDF. Therefore in these fields the continuous filters are preferred. However, they are using vacuum as the driving force for the dewatering, so that the solids stay in contact with the atmosferic conditions. Negative aspect is that only approximative 0,5 bar is available as driving force for the dewatering. With the KDF the driving force is approximative 12 times higher, giving a higher specific filtration capacity and a far lower moisture content of the dewatered product. The Amafilter Continuous Pressure Filter, type KDF, gives a lower moisture content than both classical vacuum filters and centrifuges. The improvement lying in the ranges of 5-15 wt. % ande 3-6 wt. % respectively. The solid content of the filtrate is less than 1 g/l. Energy consumption per pound of dry filtered coal is also lower.
Topic(s)
Call for proposal
Data not availableFunding Scheme
DEM - Demonstration contractsCoordinator
1800 AJ ALKMAAR
Netherlands