Design and engineering of biogas plants - The Biogas: Science, Production and Applications - page 201

Table 8.3 Choosing pipework

Key parameter Required pipe characteristics

Transported material
and pipe location

Biogas pipes made of stainless steel if the pipe is above
ground and polyethylene (PE) if below ground. Pipework
for substrates and digestate are generally PVC, PE or steel

Temperature of the
material

C. Above this,
steel should be used (e.g. after hygenisation unit)
Pressure in the pipe Pipes under pressure are usually made out of steel. If
plastic material is used, the wall thickness must be
increased. The pipe diameter varies between 100 and
150mm - big enough to prevent obstructions, but small
enough to prevent pressure losses and sedimentations.
Overflow or return pipes are generally PVC and have
larger diameters of 200-300mm (Eder and Schulz, 2006)

PVC and PE are fit for temperatures up to 60 8

and diameter is essential to avoid major problems during operation such as
clogging and abrasion.

8.4.1 Pipework

Substrates and gas are transported in pipework. Pipe material and diameter
must be chosen with regard to the transported media and its temperature,
pipe location and pressure in the pipe. The relationships between these
parameters and pipe characteristics are described in Table 8.3. All pipes
need to be protected from frost, which can be done with heat insulation and
tracing. Necessary devices in pipework are also inspection and cleaning
apertures to allow access to the problem area in the case of pipe clogging.

8.4.2 Pumps

￿ ￿ ￿ ￿ ￿ ￿

When flow by gravity is not possible, pumps convey material from one place
to another. A pump needs to be adapted to the conveying material and the
total dynamic head (TDH). Dry matter content and the risk of containing
impurities must be considered; while some pump types are very sensitive to
variations, others are relatively robust.
The total head is the equivalent height that feedstock needs to be pumped,
taking account of the suction head and discharge head (Fig. 8.8). To
calculate the TDH, head losses, caused by the friction between fluid and
pipes due to roughness, direction changes or valves, also have to be
considered. The formula is

TDH m ðÞ¼ Suction head m ðÞþ discharge head m ðÞþ friction losses m ðÞ½ 8 : 6