New methods for determining KCI in straw by dk-TEKNIK ENERGI og MILJØ

The content of water-soluble salts as potassium chloride (KCl) in straw may cause a number of different operational problems during the energy conversion in the plants. The content of potassiumn and chloride in straw varies a lot and depends among other things on the conditions during the cultivation and harvest. The colour of the straw has traditionally been used as an indication of the content of the problematic salts. The colour of the straw is however not a very reliable measure. In this project a simple and practical method for determination of the content of chloride/potassium chloride to be used in the plants is developed. Furthermore, it is shown that a measure of the total content of potassium and chloride can be obtained from the content of chloride in the straw. The achieved results in the project are based on experiments carried out on 10 different samples of straw. Most of these samples had a rather low content of potassium and chloride. This is due to the wet harvest of 2001, making it difficult to get straw with a higher content of potassium and chloride. A preliminary determination of the content of potassium and chloride in the 10 straw samples, using the standard methods of the laboratory, showed that the content of potassium (K) in the 10 samples was more than twice the amount equivalent to chloride (Cl)in potassium chloride (KCl). This means that the equivalent amount of potassium is under the half of the content of potassium in the straw if the whole amount of chloride in the straw is considered to be in the form of KCl. By comparing with previous data of straw it was concluded, that this proportion reasonably could be assumed to apply in general. That means also for straw with a high content of potassium and chloride. In the project partly an existing thermal method is tested adn partly methods based on dissolution in water of the potassium and chloride in the straw, followed by a quantification of the dissolved amounts. The thermal method is a method being developed to achieve a measure of the amount of KCl particles that might be emitted with the flue gas during the combustion of a present straw. In the project is investigated whether the metod may be used more general, that is to achieve also a measure of the content of KCl in the straw. The investigation showed that this was not possible. For a preliminary determined simple dissolution method, shaking up a portion of straw with a portion of water, the following principles of methods for a quantification of the dissolved contents of potassium and chloride were tested: Determination of the content of potassium and chloride using the standard methods; Determination of the content of potassium and chloride using test sticks; Determination of the content of potassium and chloride using ion-selective electrodes; Determination of the conductivity; Determination of the content of dissolved solids. The testing showed that the content of chloride in the straw samples was brought into solution to a satisfactory extent for the chosen dissolution method. The content of potassium was however only brought into solution, a determination by a test stick from HACH was found to be both simple and good. A corresponding simple opportunity was not identified for the determination of the potassium. As the combination of the chosen dissolution method with a determination of the chloride content by a test stick both fulfills the requirements of a simple and practical method and gives results comparable with the standard method of the laboratory, this combination was chosen to be the routine method. The method laid down by the project is thus a simple and practical method for the determination of the content of chloride in straw. The equivalent content of potassium chloride (KCl) can directly be calculated from the content of chloride. A measure for the total content of potassium and chloride can be achieved from the found rpoportion between the content of chloride and the total content of chloride and potassium in straw