Innovation in Global Power - Parsons Brinckerhoff

DEPARTMENTS
PB’s power specialists
provided R&D for the
redesign of the main
components of a dynamic
composting system. This
was a new area of work that
resulted in lower energy
consumption for our client
and an expected longer life
for its composting equipment.
Figure 1: Corridors in an opentrench
composting facility.
Figure 2: Composting machine.
PB Redesigns a Composting
Machine for Improved Operations*
By Oriol Altés, Barcelona, Spain, 34 93 5088520, altesO@pbworld.com
Manufacturing organic compost is an effective way to recycle urban solid waste (USW) and
other raw materials, such as sewage sludge and vegetable and forest residues. This can be
done by using a dynamic composting system in either open trenches or closed tunnels.
Open trench dynamic composting requires the construction of specific machinery. We are
seeing many new developments and continuous improvements in such machinery. In fact,
PB has worked closely with a client in Spain on the redesign of its operational units. Our
research and development of new solutions and improvements have led to a revised design
of the main systems of the composting machinery, including the mechanical, electromotor,
hydraulic, control, and safety systems, and the redesign of civil works for the implementation
of the machinery.
Dynamic Composting Machinery
Dynamic composting is based primarily on mixing USW or sewage sludge with other
vegetable substances to obtain the correct initial properties for density, viscosity and humidity.
The fermentation and maturing processes of this primary material take place in a group of
trenches (Figure 1), which are corridors limited by concrete
walls and a lower soleplate/ventilation system. The soleplate is
a false floor made of perforated tiles that provide adequate
ventilation to the material in the composting process. The
trenches can be in a closed industrial warehouse or in an
open one with a roof only, depending on the surrounding
environmental needs, such as odor control and other
considerations.
The composting machine moves along the concrete walls on
a rail system turning over the material with a cylindrical rotating drum
with blades as it moves (Figure 2). It is propelled with electric motors
for the translation movement and hydraulic power for the rotating
drum. Composting operations are fully automated. The machines can
be programmed to turn over material in all the trenches at the plant. An
auxiliary transfer rack guides the machine into position over each trench.
The turn over accelerates fermentation and the maturing process by
contributing to the dissipation of excessive heat/temperature and restoring
oxygen to the material. In addition, the ventilation system helps to
maintain adequate levels of temperature and oxygen. The machine could
also incorporate an on-board irrigation system. Gases emitted in the
fermentation process are captured and sent to a treatment system (washing and filtration). 1
Leaching generated is reused to wet the organic material at the beginning of the process.
*La edición en lengua española del
presente artículo está disponible
en la dirección Web de PB Network.
1 The topic of treating gases is covered in more detail in a preceding article, “Converting Landfill Gas to High-Btu Fuel” by Roger
Lemos. This is also on the web at http://www.pbworld.com/ news_events/publications/network/
91 PB Network #68 / August 2008