Patents by Inventor Douglas Charles Harper

Douglas Charles Harper has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).

  • Process for reducing formation of gypsum scale durng the washing of calcium sulphate hemihydrate crystals
    Patent number: 4049774
    Abstract: A process for reducing formation of calcium sulphate scale during the washing of calcium sulphate hemihydrate crystals by washing the crystals with a liquor containing certain surface-active agents in sufficient amount to give a concentration of from 0.0002 to 1% by weight of surface-active agent in the wash liquors.
    Type: Grant
    Filed: November 8, 1974
    Date of Patent: September 20, 1977
    Assignee: Fisons Limited
    Inventors: Douglas Charles Harper, Norman Robinson, Stanislaw Maria Janikowski
  • Method of preventing gypsum scale formation in phosphoric acid plant filters
    Patent number: 3972981
    Abstract: The anti-scaling effect of additives added to control the formation of scale during the washing of calcium sulphate anhydrite or hemihydrate crystals is increased when the additives are added as soon as possible after the wash liquors leave the crystals. The invention is of especial use in the washing of calcium sulphate hemihydrate produced during the production of phosphoric acid and is carried out by adding the additives via the central valve of the rotating pan filter on which the hemihydrate crystals are washed.
    Type: Grant
    Filed: October 25, 1973
    Date of Patent: August 3, 1976
    Assignee: Fisons Limited
    Inventors: Douglas Charles Harper, Norman Robinson, Stanislaw Maria Janikowski