Sewage sludge disposal at the Guangzhou cement plant

The cement industry has an important role in the co-processing of sewage sludge. While agricultural use only allows material recycling, co-burning in waste incineration or coal-fired power plants leads exclusively to energy recovery. If, however, the sewage sludge is used in a cement plant, it is not just burnt, but allows both material and energy recovery in accordance with the principles of waste management and recycling.

Energy sources and replacement of raw materials
Because of their composition, the non-combustible, mineral components of the sewage sludge fit well into the raw materials matrix required for cement production. They replace corresponding proportions of the individual raw material components and are permanently bound into the cement clinker – no residues accumulate. During the burning process, heavy metals are also incorporated into the clinker, which then cannot escape.
In terms of their heating value, the combustible, organic components of the sewage sludge replace a corresponding proportion of a primary fuel such as coal. The high combustion temperatures of up to 2,000°C in the cement kiln destroy the pollutants and allow optimum utilisation of energy.

State-of-the-art technology at the Guangzhou cement plant (GCPN)
Drained sewage sludge is already being thermally dried by the waste heat from the cement kiln at our GCPN plant in China, which increases its heating value substantially. The sludge then has such a low water content that it can be placed in the main furnace of the cement kiln almost in the form of powder and granules. GCPN is able to use 100,000 tonnes of drained sludge per year, making it the largest sludge co-processing facility at the cement plant in China. The technology was developed and perfected in China, with the aim of minimising the municipal disposal costs, improving hygiene conditions and reducing emissions in the Guangzhou region. The project was supported closely by the Chinese cement association, partly because the process offers great potential for improving the environmental and health situation in China.

Protecting the environment and resources
By launching this pilot project, HeidelbergCement offers a solution for sustainable disposal of municipal sewage sludge. This prevents the need for public investment in alternative but costly disposal channels. On the other hand, material and energy recovery from sewage sludge in cement plants benefits the environment in several respects: Limestone and coal are preserved as resources, which aligns with the concept of waste management and recycling. In addition, sewage sludge is classified as biomass on account of its organic components, which reduces CO2 emissions and does not compete with the nutrition of humans or animals.