Investigation of Scaling Potential in Spray Drier Applications

Reagent Selection Criteria. Thus there are a number of candidates that would be useful for controlling scale at the Turk Power plant, however to be successful the reagent must be: 1. Cost effective. Managing scale formation at the plant will require the constant addition of a reagent and its long term cost must be low. 2. Active in low dosage. This follows from both cost considerations as well as issues with regard to the performance of the spray drier itself. 3. Recyclable. A significant proportion of the ash at the Turk plant is recycled, it would be advantageous if the scale inhibitor survive the conditions of the spray drier. 4. Transparent to the Spray Drier. The reagents must not inhibit the spray drier reactions in any manner. 5. Environmentally Benign. The reagent will eventually end up in the landfill with the ash. It must be nonhazardous and nontoxic. There are a number of additives that should meet the above criteria. Most of the potential additives are reasonable priced and competitive when applied to commodities like concrete. The conditions in the spray drier itself are not that severe with maximum temperatures in the range of 250 to 270 ¢XF. Thus some of the additive should recycle which will help reduce costs. Finally, at least some scale inhibiting additives should be found that will not cause interference in the spray drier. In fact the action of the some of the reagents that inhibit flocculation may actually improve the performance of spray drier. None of the listed scale inhibitors are known to be hazardous as they would be precluded in construction or pipeline transport use. In actuality some of the listed inhibitors are used in the food industry and are in fact edible. Testing Tasks and Objectives. Task 1. Background Survey of Available Anti Scaling Additives. Objective. Identify a practical range of candidate additives for further evaluation. This effort will be directed to narrowing the evaluation of potential additives to a practical list. Information on commercially available reagents and regent packages will be collected. A literature survey will be conducted regarding the use of scale inhibitors in closely related applications will be conducted along with a more extensive patent review. The potential additives will be evaluated according to the criteria listed above using available criteria. Task 2. Performance Comparison and Evaluation of Anti-Scaling Reagents. Objective. Determine the Relative Cost Effectiveness of Anti Scaling Additives in Spray Drier System. This effort will include the testing of the candidate materials from Task 1 in bench scale test. Dosage response curves will be determined, along with minimum critical dosage levels. Two tests will be used the first being the testing of scale inhibition. This involves the dosage of a saturated solution of calcium with various levels of the reagent and measuring the residual calcium via the Schwartzenbach titration. The results are normally expressed as percent of nominal %CaCO3 inhibition, but for our purpose the test will be run at a higher pH and the results expressed as an nominal %Ca(OH)2 inhibition. This is a ¡§jug¡¨ type test. Easily run overnight and providing a large amount of comparative information. A second set of evaluations will be made for scale adherence. This will involve the use of materials, including lime and fly ash from the Turk plant. It entails the circulation of fluids in equilibrium with the scrubber material and the actual measurement of scale deposition. This test requires several days of run time will be used to verify the results of the simpler more extensive jug tests. Deliverables. „h A general survey of scale inhibiting reagents available „h An assessment of their comparative cost effectiveness in controlling scale at the Turk plant. „h A short list recommendation of candidates for testing in a lab, pilot or commercial spray drier. Two Reports, one following completion of Task 1 the second completion of Task 2.