**4. Description of the experiment**

During the experiment, birch wood chips with a fraction size of 35x8x4 mm were used as raw materials. The humidity was 9.6% (determined by the EVLAS-2 M device). Ash content 0.11%. The density of the wood is 380.95 kg/m3 . The bulk density of the chips was 187.27 kg/m3 . The calorific value of wood raw material is 17269.79 kJ/kg. The mass of wood in the basket was 200.2 g.

After loading the raw material and turning on the heater, the pyrolysis and activation chamber was brought to a thermal regime corresponding to the onset of pyrolysis (250 C). After that (55 minutes after the start of the experiment), the heaters on the steam generator and the superheater were turned on. At the same time, at the end of the pyrolysis of plant biomass (wood chips), superheated steam began to flow in the pyrolysis and activation chamber. Pyrolysis started 55 minutes after the heaters were turned on and lasted 75 minutes. The maximum pyrolysis temperature was 650 C. At the end of the pyrolysis, calcination and simultaneous activation with superheated steam for 2 hours and 30 minutes took place. The superheated steam temperature was 760 C. The total process time was 4 hours and 40 minutes. At the end of the work, the heaters were turned off. After cooling all the elements of the installation and, as a consequence, reducing the pressure to atmospheric, the lid of the pyrolysis and activation chamber was opened and the basket with samples of the finished solid product was removed.

The general view of the obtained solid pyrolysis products is shown in **Figure 14**. The mass yield of solid products was 15.5%.

After that, the basket was again loaded with wood chips and installed in the pyrolysis chamber. At the same time, the valves were removed so that during the operation of the installation in the chambers the pressure was close to atmospheric.

Then the experiment was repeated and solid pyrolysis products were obtained, the mass yield of which was 9.4%.

It can be seen that at a pressure of 8 atm, the mass yield of solid products is higher than at atmospheric pressure. This confirms the results previously obtained by the authors and described in [10, 11].

**Figure 14.** *General view of solid products of wood chips conversion.*

### **Figure 15.**

*Micrographs of samples of solid pyrolysis products obtained at a pressure of 1 atm. (a) and 8 atm. (b).*


### **Table 8.**

*Elemental composition of raw materials and charcoal obtained at different pressures.*

Investigations of the composition and properties of solid conversion products were carried out. **Figure 15** shows micrographs of samples of solid pyrolysis products obtained at a pressure of 1 atm. (a) and 8 atm. (b).

The figure shows that in the sample obtained at a pressure of 8 atm. More pores are observed on the surface than in the sample obtained at a pressure of 1 atm.

The elemental composition of the samples is shown in **Table 8**. Measurement error of elemental composition 0.1%.

The table shows that the carbon content in the sample obtained at a pressure of 8 atm. Higher than in the sample obtained at atmospheric pressure. This is consistent with the results of the studies described in [10, 11].

The bulk density of the obtained solid product was 70.85 kg/m3 . The total pore volume is 3.985 cm3 /g.

*Features of Pyrolysis of Plant Biomass at Excessive Pressure DOI: http://dx.doi.org/10.5772/intechopen.99468*

The values of the specific surface of the samples were determined. For solid pyrolysis products obtained at 1 atm., These indicators were: 50.31 m2 /g. For the products obtained at 8 atm., They are equal to: 664.99 m<sup>2</sup> /g. The iodine content in the samples of solid pyrolysis products was not observed.

All characteristics of the obtained solid products of thermochemical conversion of wood meet the requirements of the standards for activated carbon.

The results of testing an experimental installation for thermochemical conversion of plant biomass under pressure showed the effectiveness of using such equipment to obtain highly porous carbon materials, the parameters of which meet the requirements for activated carbon. The biomass pyrolysis temperature was 650 °C, the superheated steam temperature was 760°C. The total time of the activated carbon production process was 4 hours and 40 minutes. Activation time 2 hours 30 minutes. The mass yield of the obtained solid product corresponds to 15.5%. According to the indicators revealed, the resulting product meets the requirements of the standards, which makes it possible to draw a conclusion about the possibility of using the selected technological scheme for creating industrial samples of pyrolysis equipment for producing activated carbons from woody biomass.

### **5. Conclusion**

The paper describes the methods of obtaining wood (highly porous carbon materials) based on plant (wood) raw materials, and the equipment used to implement these processes, the use of charcoal. The conclusion is made about the advantage of obtaining charcoal under excess pressure.

An experimental study of pyrolysis of birch chips on a laboratory bench in the pressure range from 0.1 to 0.7 MPa showed that an increase in pressure at which pyrolysis is carried out promotes an increase in the mass yield of charcoal and an increase in the carbon content in it. At the same time, there is a decrease in the calorific value of the resulting charcoal, which is due to the release of oxygen-containing components from the porous structure of coal, which have a higher calorific value in comparison with pure carbon.

A description of the developed and manufactured experimental setup is presented, which consists of a steam generator, a superheater, a pyrolysis and activation chamber, a cooler with a heat exchanger with forced convection, which are interconnected sections. Experiments were carried out confirming that excessive pressure increases the mass yield of solid products of thermochemical conversion of plant biomass. Were determined the physical parameters of the obtained solid products of pyrolysis and physical activation at an excess pressure of 0.8 MPa.
