New Clathrate Hydrates for Second Generation Freeze Concentration Applicaiton in Paper Industry, 1997 Papermakers Conference Proceedings

Scarce fiber resources and increased environmental pressures have promoted the paper industry to look for new technologies for pulp manufacturing, fiber bleaching and effluent treatment. Zero effluent discharge from BCTMP mill has attracted greater interest from the industry. Freeze concentration can be an important part of an integrated effluent treatment system.

This study reviews the past and current technology used in freeze concentration for the pulp and paper industry. The first practice in pulp and paper industry using freeze concentration was using ice as a separating agent in a Louisiana-Pacific mill. Several drawbacks were discovered during this practice, including washing water freezing at 0°C, ice formation and plugging in the transportation pipe, difficulties with crystal size control, and high concentration of fiber. This process was proven to be successful in the lab and pilot scale, however, it had many operational problems in the actual application. In order to solve these problems, a new approach to utilize freeze concentration is proposed in this research.

Clathrate gas hydrates, instead of ice, will be used to separate the water from the rest of effluent. Clathrate gas hydrates are solid solutions formed between water molecules and gas molecule/molecules under proper temperature and pressure conditions.

Gas molecules reside inside the cavities formed by water molecules as crystal lattice structure. Unique thermodynamic equilibrium properties differ this process from that of ice. Washing can be performed at above 0°C along with effective crystal size control and plugging problem can also be effectively controlled. High purity water can be recovered upon dissociation of gas hydrates while majority of gas molecules can be recovered.