Process and device for converting biomass to gaseous products

Abstract

A device for converting biomass with a water content of at least 50% to gaseous products includes a reactor filled at least partially with a packing including at least one filler body for accommodating supercritical water and a hydrothermal molten salt. A heater is arranged to heat up the reactor and its content. A first feeding pipe is coupled to the reactor to feed water and salt solution into the reactor. A second feeding pipe is coupled to the reactor to feed to biomass into the reactor. A discharge pipe is coupled to the reactor to discharge gaseous products from the reactor. An outlet is proved in the bottom of the reactor for removing portions of the molten salt.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims the priority of the German Patent Application No.: 10 2008 028 788.1, filed on Jun. 17, 2008, the subject matter of which is incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]The invention relates to a process and a device for converting wet biomass, meaning biomass having a water content of at least 50%, into gaseous products.[0003]For generating energy from wet biomass through thermolysis or thermal decomposition, supercritical water is often used at temperatures and pressures exceeding the critical point of the water (22.1 MPa and 375° C.). Whereas organic substances are dissolved easily in supercritical water, the inorganic salts precipitate out and can result in clogging up the reactor.[0004]A lean reactor is known from the document by N. Boukis, U. Galla, V. Diem, E. Dinjus, entitled Biomass gasification in supercritical water: First results of the pilot plant, published in: A. V. Bridgewater, ...

AI Technical Summary

Benefits of technology

[0052]if the molten salt comprises an alkali salt or a salt mixture where at least one component is an alkali salt, the reactivity of the biomass can additionally be increased during the period of heating up the molten salt from the pre-heating to the reaction temperature, such that the bound carbon atoms contained in the biomass are converted, if possible completely, to CO2 and CH4;

[0053]as a result of the continuous operational control, malfunctions of the system that are caused in particular by pressure fluctuations are avoided;

[0054]owing to the counter-flow principle within the packing, the salts are absorbed efficiently and it is possible to process even biomasses with high salt loads since fresh molten salt comes in contact with a solution depleted of salts and will extract even the last amounts of salt from this solution—the bound salts can thus be removed from the reactor without affecting the operation; and

[0055]the filler bodies in the packing increase the exchange surface between the hydrothermal melt and the biomass-containing solution.

Problems solved by technology

Whereas organic substances are dissolved easily in supercritical water, the inorganic salts precipitate out and can result in clogging up the reactor.

However, this process is slow and the reaction already starts in the heat exchanger tube, as soon as the necessary temperature is reached.

According to an alternative embodiment, the preheated and concentrated biomass is fed together with the supercritical water into the reactor, which may require in some circumstance an unfavorable ratio between suspended biomass and supercritical heating water.

As a result, the heating process is accelerated and the start of the reaction is moved into the reactor, but most of the salts are precipitated out during the operation in an uncontrolled manner and are hard to remove.

However, the same problems with respect to the salt formation and the precipitating out occur with a pressure vessel as can occur under reactor conditions.

In contrast, the gasification of a biomass is endothermal and a quenching is energetically not acceptable.

The forming of charcoal or coke can furthermore not be prevented completely during the conversion with dry molten salts.

However, the latter advantage is achieved at the expense of higher corrosiveness.

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