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Content archived on 2024-04-15

IMPROVEMENT OF THE DUAL FLUIDIZED BED WOOD FAST PYROLYSIS GASIFICATION PROCESS : USE OF CATALYST AND OPTIMIZATION OF PARTICULATE SOLIDS CIRCULATION TECHNIQUES.

Objective

AN UNDERSTANDING OF THE ROLE OF CATALYSTS (OR THEIR CONSTITUENTS) AT THE VARIOUS STAGES OF GASIFICATION OF WOOD BY PYROLYSIS WILL MAKE IT POSSIBLE TO MODIFY AND THUS TO IMPROVE THE PROCESS BY APPLYING THE RESULTS OBTAINED ON THE CATALYSTS IN THE LABORATORY.
A new type of pine barks catalytic pyrolysis gasification pilot plant (20 kg/h barks capacity) has been designed and the pyrolysis gasification process improved.

The initial fast pyrolysis gasification process is a dual fluidized bed system with a pyrolysis fluidized bed where wood devolatilization reaction occurs and a char cacination circulating fluidized bed where the char combustion occurs. There is a continuous circulation of a particulate soild heat carrier between the 2 reactors.
A specific characteristic of process is a special contacting zone above the pyrolysis fluidized bed so called SATURNE.
The gas coming out from the pyrolysis fluidized bed (which contained tars) flows through the SATURNE countercurrently to the hot heat carrier which trickles down. The contact gas and heat carrier in that zone enhances the detaring action.
An industrial pilot plant (500 kg/h pine barks capacity, dry basis) was erected in a pulp mill and successfully tested in 1984 and 1985.

Improvement in the process can be achieved in 2 directions: optimizing the heat carrier circulation in such way that it will not be difficult to control the mass flow rate of heat carrier; using catalyst as heat carrier for lowering the temperature over the detaring zone.
2 main studies have taken place concerning the heat carrier circulation techniques, and the potential catalytic effect of the heat carrier.

The study of circulation solid techniques showed that Kunii's 4 compartment reactor concept was well suited to the process, particularly because the control of the solid circulation rate is easy and the gas leaks between the compartments are low enough to prevent any explosion risk inside the reactor. Different possible catalysts were tested for tar craking and it was concluded that decarbonated or carbonated dolomite was well adapted to the process. This catalyst may be used as a heat carrier because it is easily fluidizable, has a long life and a good catalytic efficiency on tar cracking.

A new type of pyrolysis fluidized bed reactor has been designed incorporating the catalytic heat carrier.
This reactor will be more compact and less expensive: the heat carrier mass flow rate will be easier to control and the pyrolysis gas will be well detared in order to be used in an engine motor for example (after dedusting).
PHASE 1: STUDY OF THE CATALYTIC REACTION (NANCY UNIVERSITY).
THE INITIAL RESULTS OBTAINED USING THE DOLOMITE WILL SERVE AS A STARTING POINT AND THE AIM WILL BE TO ANALYSE THE INFLUENCE OF THE DOLOMITE AND ITS VARIOUS CONSTITUENTS ON EACH OF THE STAGES OF THE REACTION.

PHASE 2: STUDY OF THE ADAPTATION OF THE CATALYST TO THE MODIFIED PROCESS (UN/TNEE)
THE STABILITY OF THE CATALYST WILL BE STUDIED DURING SUCCESSIVE ACTIVITY - REGENERATION CYCLES AT THE LABORATORY AND PREPILOT STAGE FROM THE VIEWPOINT OF THE MODIFICATION OF EITHER THE PURELY CATALYTIC EFFECT, EG POISONING, OR THE PHYSICAL STRUCTURE (SINTERING, ATTRITION, MECHANICAL ABRASION RESISTANCE, ETC...)

- PHASE 3: STUDY OF CIRCULATION OF SOLIDS (UTC/TNEE).
THE AIM WILL BE TO DEFINE THE BASIC FEATURES OF THE LINKAGE SIPHONS AND CIRCULATION MEMBERS OF THE CATALYST BETWEEN THE PYROLYSIS AND THE CALCINATION - REGENERATION REACTORS. THE STUDY WILL BE CONCERNED WITH THE OPTIMIZATION OF TRANSPORT (AERATION FLOW, LOAD LOSSES, ETC...) AND THE STANDARD OF IMPERVIOUSNESS BETWEEN THE REACTORS. RESEARCH WILL THEREFORE FIRST FOCUS ON THE FLOW OF PARTICULATE SOLIDS IN THE VERTICAL, HORIZONTAL AND INCLINED TRANSFER LINES. THESE LINES WILL CONTAIN THE AIR REQUIRED TO ENSURE AT THE SAME TIME BOTH THE FLOW OF THE SOLID MATTER AND THE CONTROL OF ITS FLOW. THE FLOW PATTERNS AND LAWS UNDER DIFFERENT CONDITIONS AT THE PRESSURE LIMITS AND WITH DIFFERENT GEOMETRIC CONFIGURATIONS WILL BE STUDIED, AS WILL THE EFFECT OF THE POSITION OF THE AERATION POINTS. THIS WILL MAKE IT POSSIBLE TO ANTICIPATE THE CONDITIONS FOR LINKING THE DIFFERENT SECTIONS TO DEMAND IN THE LIGHT OF THE CONDITIONS AT THE PRESSURE LIMITS AT THE LINE ENDS. PARTICULAR ATTENTION WILL BE PAID TO THE DIRECTION OF FLOW OF THE INTERSTITIAL GAS WITH A VIEW TO SAFEGUARDING DIRECTIONAL IMPERVIOUSNESS IN INDUSTRIAL INSTALLATIONS IN WHICH SUCH LINES CONNECT VESSELS WITH INCOMPATIBLE ATMOSPHERES.

PHASE 4: PRE-PILOT STUDIES (TNEE):
CATALYTIC PYROLYSIS TESTS WILL BE CARRIED OUT ON CONTINUOUSLY USING PRE-PILOT EQUIPMENT WITH A CAPACITY OF ABOUT 10 TO 20 KG.H OF WASTE WOOD. THE PLAN FOR THIS PILOT STUDY WILL TAKE ACCOUNT OF EXPERIENCE WITH THE INDUSTRIAL PILOT STUDY OF CIRCULATION BETWEEN HIGH-TEMPERATURE FLUIDIZED BEDS. IT WILL BE DESIGNED WITH THE AIM OF COMPACTNESS, SIMPLICITY AND OPERATING ECONOMY. THE TESTS ON THIS EQUIPMENT WILL MAKE IT POSSIBLE TO:

-TEST THE ADVANTAGES OF THE NEW REACTOR GEOMETRIES AND LINKAGE SIPHONS;
- VERIFY AT A HIGH TEMPERATURE THE OBSERVATIONS MADE IN THE COLD STATE;
- VERIFY THE OPTIMUM CATALYTIC BEHAVIOUR DEVELOPED IN THE LABORATORY (PHASES 1 AND 2) DURING HIGH-TEMPERATURE CIRCULATION BETWEEN THE TWO REACTORS (ABRASION, EROSION, ETC...);
- CONFIRM THE CHARACTERISTICS OF THE PYROLYSIS GAS OBTAINED IN THE PRESENCE OF THE CATALYST;
- TEST THE SERVICE LIFE AND REACTIVITY OF THE CATALYST.

THE TESTS WILL BE CARRIED OUT MAINLY USING PINE BARK, WHICH WILL MAKE IT EASIER TO COMPARE PYROLYSIS WITH AND WITHOUT A CATALYST.

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Tunzini Nessi Entreprises d'Equipements SA
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