Reuse of waste glasses in cement production - a DEMOS project)  

Project Title: Reuse of waste glasses in cement production - a DEMOS project

Applicant: The Hong Kong University of Science & Technology

Total Approved Grant: $127,500 (jointly funded by ECF and WWGF on an equal share basis)

Duration: 5/11/1999 - 31/10/2000

Status: Completed

Scope:

This is a sequel to Project No. 14/97 in which the chemical composition of 32 types of glasses were characterized and proved that it was possible to use the waste glass as one of the raw materials in cement production. This project aims to collaborate with one local cement manufacturer to conduct a set of ill trial experiments to demonstrate that waste glass can be reused in industrial scale.

Summary of the Findings: We have conducted plant experiments using waste glass in cement production. The waste glass used was mainly beverage and beer bottles that contained significant amounts of alkali. For the two plant trials conducted, one trial was performed with the rate of waste glass recycled at 1 tonne/hour for a total raw material feed rate of about 280 tonne/hour; and the other was with 2 tonnes/hour of waste glass. The first trial was conducted for 24 hours and the second for over 60 hours. The chemical analysis of the clinker produced did not show any significant changes in composition compared with the baseline values. The alkali content increased slightly but was well below the value specified for high quality Portland cement. The air quality measured in the stack did not show any change from the base line and met the discharge permission standard specified by the Environmental Protection Department of the Hong Kong SAR government. The physical properties of the cement produced were tested and found to be comparable with cement when no waste glass was added.

This project demonstrated that the proposed method of recycling waste glass is feasible. Provided the amount of waste glass to be used as the feed to the cement manufacturing process is within the design limits, the properties of the cement produced will not be affected. The gaseous emission from a cement production plant using recycled glass in the feed will satisfy the government standards for discharge.