Method for conducting a hydrothermal carbonization reaction

Abstract

During hydrothermal carbonization, biomass is converted to biocoal. The reaction yield depends on the reaction conditions, including duration of the carbonization reaction or time period within which the slurry composed of water and biomass remains in the reaction tank and is exposed to pressure and temperature. These conditions should be selected so that the greatest possible dry residue of carbonized material remains in the slurry. It has been shown that the dry residue amount changes during the carbonization reaction with a curve that is similar, to a great extent, to that of the slurry pH value. Because determining the dry residue is difficult during the ongoing reaction, but determining the pH value can be easy during the entire reaction period, the reaction is terminated at a maximum of the pH value corresponding to a maximum of the biocoal dry residue, to the greatest possible extent.

Claims

1. A method for conducting a hydrothermal carbonization reaction comprising: (a) supplying biomass to a reaction tank; (b) creating reaction conditions with regard to pressure and temperature required for allowing a hydrothermal carbonization reaction to take place by introduction of steam and maintaining the reaction conditions for a reaction period; (c) forming a slurry during the reaction period from the steam and the biomass that are introduced; (d) monitoring the slurry with regard to progression of pH value of the slurry; and (e) terminating the hydrothermal carbonization reaction as soon as a determination is made that a maximum of the pH value has been reached.

2. The method according to claim 1, wherein the progression of the slurry is determined continuously or at discrete time intervals, using at least one measurement probe assigned to the reaction tank, and noted in a database, wherein a process controller compares a current pH value with preceding measurement values from an identical measurement series within the reaction period, and triggers a termination signal when a decrease in pH value that follows an increase phase occurs.

3. The method according to claim 2, wherein the at least one measurement probe is disposed close to a bottom of the reaction tank.

4. The method according to claim 1, wherein the progression of the slurry is determined continuously or at discrete time intervals, using at least one measurement probe assigned to a bypass of the reaction tank, and the pH values are noted in a database, wherein a process controller compares a current pH value with preceding measurement values from an identical measurement series within the reaction period, and triggers a termination signal when a decrease in pH value that follows an increase phase occurs.

5. The method according to claim 1, wherein the slurry is mixed in the reaction tank during the reaction period.

6. The method according to claim 1, wherein measurement begins when the reaction conditions of hydrothermal carbonization, with regard to pressure and temperature, have been reached and biomass and steam have already been introduced into the reaction container.

7. The method according to claim 1, wherein the hydrothermal carbonization reaction is terminated by bringing the slurry out of the reaction tank into a cooling tank via pumping or pressure equalization.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other objects and features of the invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.

(2) In the drawings:

(3) The sole FIGURE shows a diagram of an exemplary progression 1 of the dry residue in %, using a solid line, and, in direct relation to this progression, the progression 2 of the pH value, in a dot-dash line. The first or left upright axis, indicated as pH, represents the pH value, while the second or right upright axis, indicated as TR [%], represents the dry residue in percent. The longitudinal axis is a time axis, with the numbers indicated representing information in minutes.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(4) The reaction represented in the sole FIGURE starts at the time point t=0 min. First of all, it can be determined that at the beginning of the reaction, the pH value decreases greatly and already reaches a minimum at t=15 min. The dry residue, in contrast, decreases more slowly and only reaches its minimum at about t=60 min. From here on, both the dry residue and the pH value increase uniformly, and both reach a maximum at t=180 min.

(5) The diagram also shows the further development of the two values, in the event that the reaction is not conducted according to the invention. Then pH value and dry residue will clearly decrease and assume a more or less constant value at about t=240 min. Although the dry residue amounts to as much as 17% at its maximum, it lies at 12 to 13% in the case of a longer duration, in other words one-fourth less. Terminating the reaction, according to the invention, when the maximum of the progression of the pH value has been reached, however, ensures that the dry residue does not decrease due to a lack of further reaction. At this point in time, according to the invention, the slurry is removed from the reaction tank, cooled, and subsequently separated from the process water.

(6) What has been described above is therefore a method for conducting a hydrothermal carbonization reaction, which allows a clear reduction in the dwell time of the slurry in the reaction tank, and, at the same time, brings with it a greater yield of biocoal and thereby greater pollutant elimination from the process water.

(7) Although at least one embodiment of the present invention has been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.