Date of Award


Document Type

Master Thesis

Degree Name

Masters of Science (Research)


Chemical Engineering

First Advisor

Mr. John O'Shea

Second Advisor

Dr. Aisling O'Gorman

Third Advisor

Mr. Peter Davies


Gypsum is produced as a by-product during the citric acid production process at ADM Ringaskiddy. The particle size and filterability of the gypsum has a critical bearing on the overall citric acid production rate. Prior to August 1996, research in the area of gypsum crystal optimisation at ADM had concentrated on the application of vortex mixing to perform the gypsum formation reaction. While the gypsum crystals produced with vortex mixing were found to be desirably clear of microcrystalline gypsum, the crystals were considerably smaller and more difficult to filter and wash. This research project sought to retain the advantages conferred by the vortex mixer but subsequently grow larger gypsum crystals in order to at least reclaim the design gypsum filtration capacity. The development of a comprehensive database enhanced the technical understanding of the gypsum production process. A pilot laboratory experimental rig was designed and constructed to simulate the plant results and facilitate intensive experimental trials. Experiments performed on the gypsum slurry (downstream of the vortex mixer) demonstrated that once the gypsum c^stals have been formed, the crystal size cannot be increased. The most significant improvement in gypsum crystal size was obtained when the reaction was performed at a low specific gravity. The addition of impurities to act as habit modifiers did not succeed to influence the crystals as found by researchers in the phosphoric acid industry. Plant trials verified that the gypsum crystal size and filtration rates are much improved when the vortex mixer is off-line but the level of microcrystalline gypsum is higher. The low level of microcrystalline gypsum which is found with the vortex mixer on-line, was obtainable in the laboratory trials due to the adequate sulphuric acid dispersion system within the reactor.


M.Sc. in Chemical and Process Engineering.

Candidate for the Degree of Master by Mode A (Research and Thesis).

Submitted to the National Council for Educational Awards, April 1999.

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