RENEWABLE ENERGIES: SYNGAS, PYROGASIFICATION,
HYDROTHERMAL GASIFICATION, HYDROGEN

Renewable energies

SOCLEMA offers sampling systems for all types of renewable energies such as pyrogasification and hydrothermal gasification.

Various systems are available, including a TAR PROTOCOL sampling system and a syngas purification system for chromatographic analysis.

As a sampling specialist, SOCLEMA reminds you of the TAR PROTOCOL sampling guidelines.

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Pyrogasification, an efficient energy source that complements methanization

Pyrogasification is one of the 3 processes used to produce biomethane, a non-fossil renewable energy. It's an ancient technique that was once used to produce charcoal. In the 19th century, it was also used to produce "town gas" from hard coal.

Complementary to other renewable energies, pyrogasification is a key component of today's ecological transition. Pyrogasification uses a thermochemical process to transform relatively dry organic residues such as wood and other waste materials into a combustible gas that can be used in a variety of ways. The energy generated by this process can be directly stored and injected into existing networks.

The gas produced by this solid biomass gasification process is called syngas.

Pyrogasification: a 2-stage process:

1- Pyrolysis: thermal decomposition process that produces, under the effect of heat and in the absence of an oxidizing agent :

- solid compounds: char and biochar

- liquid compounds: pyrolysis oils

- gaseous compounds: synthesis gas (a mixture of H2, CO, CO2 and CH4)

2- Gasification: a process which, through complex thermochemical reactions, converts the liquid and solid parts into a combustible gas rich in CO andH2 called "syngas" - Cogeneration allowing the simultaneous recovery of electricity and heat (possibility of significantly improving electrical efficiency compared with a conventional process involving the direct combustion of biomass).

- Direct replacement of natural gas for certain industrial applications such as glass melting

- Production of biomethane (also known as synthetic natural gas) using the methanation process.

Tars produced by pyrogasification

The resulting synthesis gas carries with it, under the effect of high temperatures and in an uncontrolled manner, heavy organic compounds generated by thermal decomposition and known as tars. These tars condense easily on cold spots, fouling pipes and reducing heat exchange efficiency. Tars can also form coke through coking or soot through polymerization.

Although tars are not the only source of poisoning (particulates, metal salts, inorganic sulfur, chlorine and nitrogen compounds), they remain the most difficult pollutant to eliminate.
Tars are defined in different ways. Generally speaking, " Tars " refer to a complex mixture of aliphatic or aromatic hydrocarbons of one or more rings, which may or may not contain a heteroatom.
The composition of tars in a synthesis gas depends directly on operating conditions (temperature, pressure, oxidizing or non-oxidizing atmosphere, residence time), the type of reactor used and the nature of the biomass.

However, the analysis of tars, and in particular their sampling in extreme environments (high temperatures and pressures, high humidity), is proving to be a delicate task. The difficulty lies in obtaining a sample which, under laboratory conditions, is as representative as possible of synthesis gases.

SAMPLING SYNTHETIC GASES WITH TAR PROTOCOL

The reference method for tar sampling is called the Tar Protocol.

This technique is based on discontinuous sampling of synthesis gases containing particulates and tars under isokinetic conditions.

The sampling system consists of several trapping devices: a heated particle filter, a condenser and a series of bubblers containing solvents. The sampling lines are heated to partially prevent tar condensation before the sampling devices.

The sampling process consists of 4 modules and sub-modules.

Module 1 consists of a sampling valve system and a heated isokinetic rod, which enables gases to be sampled from both pressurized and non-pressurized reactors. Sampling lines are generally maintained at temperatures above 350°C to minimize condensation of heavy tars.
Module 2 consists of a gravimetric filter to recover particles from the reactor outlet. These particles could lead to clogging of the downstream sampling media (condenser and bubblers).
In Module 3 , the tar-collecting bubblers are placed in different baths at temperatures ranging from 20 to -20°C. The baths absorb the heat released by the cooling and condensation of the gases. Direct condensation of liquid effluents without a dilution medium (cold trap only) can lead to reactions between the trapped compounds, so a solvent is placed in each of the bubblers to absorb these compounds and avoid any parasitic reactions.Isopropanol was identified as the most suitable solvent for tar collection, due to its low toxicity and ability to solubilize tars for collection. Immediately after sampling, the contents of the bubblers are stored in a bottle which is kept hermetically sealed at a temperature below 5°C for subsequent analysis.
Module 4 is used to measure and adjust gas parameters.

The gas flow rate is kept constant by means of a vacuum pump. It is important to ensure that the sampling rate is not too high in relation to the cooling and adsorption capacity of the bubblers.