Page 76 - Industrial Plants

Figure 1 -
General process
of AD

Digestate is heat treated to kill any dangerous heavy-duty vehicles (HDV) due to its high energy
pathogens and can be used as an organic soil density. HDVs require about five-times more power
amendment without further processing, or the than passenger vehicles to achieve viable operating
digestate’s value can be increased by drying it, mileage.
removing certain nutrients, and pelletizing. To supply this power, an HDV can either rely on fuels
The RNG from AD facilities is pipeline-quality and fully or batteries. Unfortunately, even the most advanced
interchangeable with conventional natural gas - it is batteries cannot compete as they have a 30-to-50-
the only renewable energy source that can be used times smaller energy density than RNG. For an
with existing natural gas-pipeline infrastructure. average HDV, this equates to a battery size of around
This is a crucial distinction of RNG, as it enables both 800-1000kWh to deliver 800km (500 miles) of range
the political and economic sphere to transition to a and, at current energy densities of state-of-the-art
sustainable fuel base by leveraging existing pipeline batteries, the necessary battery weight would be
infrastructure. Like conventional natural gas, RNG can around 5,000-6,000kg, which decreases payload
be used as a transportation fuel in the form of capacity. In fact, for equal ranges, battery-powered
compressed natural gas (CNG) or liquefied natural trucks can carry ~40% less payload than trucks
gas (LNG). powered by fuels.
The RNG present in the Biogas is extracted and
concentrated via a biogas upgrader process The second end-product of AD is digestate, which is
separating. an organic soil amendment that consists of broken-
down organic matter. Digestate is similar to compost
Carbon dioxide, Water, Hydrogen Sulfide in chemical and physical composition, but it is
and Particulate CO2 and Water can be re-cycled. produced in an anaerobic environment rather than the
This form of renewable natural gas RNG is ideal for oxygen rich environment needed for compost.

INDUSTRIAL PLANTS - September 2021
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