Cleaner Technology Projects in Denmark 1997
Chalk from Aggersund
Aggersund dybdekridt
Arbejdsrapport nr. 72, 1997, Miljøstyrelsen
The pilot-project has been carried out by Agersund Kalkværk and Dankalk A/S. The purpose of the report is to examine whether investing in cleaner and more energy-saving technology will make it possible to produce competitive and environmentally friendly final products, which can be disposed of to desulphurizing of waste gasses from power stations with oil and coal heating, and which can be used as fill material for several industries in Denmark and on the export-markets.
Today the chalk is primarily used as agricultural lime and as an additive for animal fodder. However, during the last 30 years Dankalk A/S has extended its activities to include the industrial sector in which the kiln-dried limestone is used as fill material for rubber, carpet treatment, asphalt, adhesive cement, putty, ceramic and paint industry. The annual excavation of limestone at Aggersund is over 500,000 tons.
A negative development in the demand for limestone products within the agricultural sector during the 1980’s gave the limestone quarry the incentive to look for new markets and new products.
A law dated 5. April 1989 on limitation of emission from coal-fired power plants exposed a new demand for limestone products for cleaning exhaust gasses. Initially Dankalk A/S tried to enter this market with kiln dried pulverised limestone but was rejected because of too many impurities in the product from an excessive content of Silisium (SiO2). It was then decided to develop and test limestone products in a pilot plant with the purpose of making new developed limestone products to meet the demands for desulphurisation of exhaust gasses, cleaning water, neutralising acids etc. Along with this enterprise considerations would be made whether it was possible to achieve the incentive to carry out final and large investments in new methods and cleaner technology.
Raw material investigations were performed to analyse the fineness and extension of the raw material i.e. to find the boundaries for raw material with a high content of calcium carbonate.
The deposit at Aggersund is a soft, fine-grained and smudging limestone chalk. The raw material is firm and coherent but still porous.
The investigations showed that the upper layer limestone contains too many impurities to make it feasible to exploit this part of the deposit. The main conclusion was that the usable raw material with an acceptable high content of calcium carbonate must be extracted from level - 6 to - 20 which means that the best limestone is below the ground water table.
Aggersund Dybdekridt is used as a desulphurization absorbent in the form of "crumbles". Crumbles are precipitated chalk having undergone an upgrading process in hydrocyclones during which, among other things, 99 percent of the flint has been removed.
Residuals from the processing are re-cycled into agricultural lime so that all raw materials are used.
The combination of new and known technology in the process has reduced the energy consumption for the whole production process, especially the change from previous kiln-dried limestone into a non-thermal dewatering process using a membrane filterpress. Furthermore the initial tests using the crumbles show big energy savings for the end users.
Crumbles is less abrasive than coarse, crystalline limestone the use of which means longer life and lower operating costs for desulphurization process components in oil- and coal fired power plants.
Characteristics like high reactivity and porosity of the new semi-manufactured products have resulted in a high rate of transformation for upgrading processes in which the products go through a water phase. By the same token the quality of residuals like gypsum is increased because of lower content of residual calcium.
Crumbles may be transported in an ordinary truck or a coaster as they are an environmental friendly and easily handled product. The transportation to the end user by sea furthermore contributes to a lower energy consumption and consequently less pollution and less loads on highways. A typical coaster cargo equals to 40 truckloads.
Tests have been performed at three coal-fired power plants using crumbles from Dankalk to desulphurized exhaust gasses.
Overall the tests have shown many advantages and few drawbacks:
 | Unproblematic suspension, feed and adjustment |
| Improved adjustment than with dry limestone as crumbles are dissolved at feed point and are more reactive than limestone |
| Lower content of residual calcium carbonate in the gypsum |
| Cleaner gypsum |
| High reactivity of the Dankalk a/s chalk saves a 500 kW recirculation pump with the same gypsum quality |
| Gypsum particle grain size is smaller which makes dewatering and waste water cleaning more difficult but not impossible |
The pilot project and tests at oil- and coal fired power plants have shown that the new product from Dankalk A/S has lived up to expectations and will be accepted by future users.
Based on these facts the board of DLG has granted the necessary funds for a full-scale project for production of "deep-chalk" products.
Author/ institution
Charlotte Olsen, Dankalk A/S
Birger Rosberg, BR Consult
This report is subsidised by the National Council for Recycling and Cleaner Technology
ISSN no. 0908-9195
ISBN no. 87-7810-868-3