Title [1/13]

Vadim A. Kuznetsov

Institute for

Electrophysics

and Electric

Power RAS

FROM DOWNDRAFT GASIFICATION OF WOOD IN THERMAL PLASMA OF AIR TO DEVELOPMENT OF MULTI-

GAS PLASMA TORCH

Role of Plasma in Gasification [2/13]

0.41 1.53

0.59 1.53 0.41

Paraformaldehyde could be gasified by air at 1500 K…

but efficiency will be about 67.7 % and syngas will be diluted.

To avoid these setbacks often oxygen is used instead of air...

but energy consumption will increaseand syngas will not stop being diluted.

0.29 0.71 0.29

LOW BIOMASS ENERGY

CONVERSION RATE

HIGHER BIOMASS ENERGY

CONVERSION RATE

AND INDIRECT CONSUMPTION

OF ELECTRICAL ENERGY

Role of Plasma in Gasification [3/13]

142.2 kJ/mol

Direct energy supply to the gasification process

makes possible to produce undiluted syngas.

HIGHEST BIOMASS ENERGY

CONVERSION RATE

AND DIRECT CONSUMPTION OF

ELECTRICAL ENERGY

Plasma gasification of wood

(LHV ~13.9 MJ/kg) by air plasma

at 1500 K & 1 atm.

The more energy is

supplied the less

oxygen is required to

maintain to process

temperature.

Plasma provides new controlled process

parameter – ENERGY CONSUMPTION.

High efficiency of energy transfer is a main

advantage of plasma. The only direct energy

supply is heating of oxidizers which is limited to

temperatures below 1000 °C due to efficiency

reduction.

Main Advantages of Plasma [4/13]

An electricity consumed by

plasma torch will be reproduced

with a surplus by combined cycle.

An electrical energy consumed by

plasma torch will be transformed

to the energy of liquid fuels.

Disbalance of energy prices in US

(average of 2013):

Electricity – 18.9 $/GJ

Liquid fuels – 34.8 $/GJ

Plasma can stabilize gasification

of wastes with variable

composition and LHV.

Plasma could be supplied to any

part of the gasifier and thus

increase local temperature.

Plasma is a highly reactive

oxidizer due to high content of

radicals and monatomic gases.

Plasma could be generated from

industrial gases (Air, H2O, CO2).

Experimental Installation [5/13]

1 – Gasifier; 2 – Plasma Torch; 3 – Afterburner; 4 – Duty Torch; 5 – Cyclone; 6 – Spray Scrubber;

7 – Packed Bed Scrubber; 8 – Exhaust Fan; 9 – Stack; 10 – Mass Spectrometer; 11 – Feeding System;

12 – Syngas Output Pipe; 13 – Ash Removal and Quenching Device. Process Steps: I – Accumulation;

II – Evaporation; III – Pyrolysis; IV – Oxidation; V – Reduction; VI – Unreactive; VII – Ash Removal.

Case:

D = 1.6 m

H = 4.2 m

Shaft:

D = 0.6 m

(IV-VI) = 1.9 m

Experimental Results [6/13]

Wood loading started load after 8 hours of charcoal

gasification at average air flow rate ~169.2 kg/h and

plasma energy supply ~67.7 kW.

Four distinct regimes could be considered: I - 8.00-9.16 h,

II - 9.23-10.06 h, III - 10.18-11.43 h, IV - 11.65-12.69 h.

Regimes I & II are not stable because hydrogen content

shows steady growth.

~351.55 kg of

wood was loaded

since 8 hours.

There are only ~2.29 hours of data for plasma gasification.

Oxygen and argon contents are near the detection level.I

II

III

IV

I

II III

IV

Experimental Results [7/13]

Evolution of temperature suggests unstedy thermal

balance on all regimes despite stable syngas composition.

Which means that gasification process takes place much

closer then 77 cm to the plasma injection zone.

I

II

III IV

At the outlet pipe syngas still contain some H2O and CO2

which means that charcoal bed is affected.

Syngas flow rate was calculated assuming that feed’s

nitrogen content is neglectable which is true for a wood.

I

II

IIIIV

One part of feed which was transformed to syngas is

shown by blue line. Other part of feed was transformed to

steam. Steam content of raw syngas was not measured.

Experimental Results [8/13]

If dashed lines are higher than solid lines of the same

color and the distance between black lines is twice bigger

than distance between red lines (if mass balance

suggests water as a unaccounted mass flow) regime

could be considered as a unaffected gasification of wood.

This is true for 13.10-13.22 hours with 10 % accuracy.

I

II III IV

This means either the presented results show rather

plasma gasification of mixed feedstocks than a wood

processing or there is an error in syngas measurements.

Regime III IV

Air/Syngas, kg/m3 0.525 0.573

Energy/Syngas, MJ/m3 1.323 0.851

H2 30.2 27.8

CO 25.7 23.8

CO2 7.8 8.9

N2 35.4 38.7

LHV, MJ/m3 5.83 5.37

Summarized process parameters (m3 at 25 °C and 1 atm).

The distortion in mass balance could be caused by

charcoal bed.

Discussion on Energy and Mass Disbalance [9/13]

Two major factors afflict results.

1. Oxidation by CO2 and H2O of coke bed which

was not originated from pyrolysis of wood.2. Heat losses in the reduction zone.

Gasification was not in stoichiometric regime and it

rarely is thus presence of CO2 and H2O unavoidable.

Volume between plasma inlet and syngas outlet is

about 0.67 m3 (contain about 126 kg of charcoal).

The sharp drop of temperature at the transition from

charcoal to wood gasification implies high reactivity of

wood and high temperatures in the mixing zone (about

1500-1700 °C considering oxidation of volatiles).

8 hours is not enough to reach stationary thermal

regime on this gasifier of at a low throughput.

The following steps should be done to resolve these issues:

- Decrease volume of the reduction zone;

- Increase both power of plasma torches and oxidant flow rate.

Unfortunately the increase of power and flow rate will took a full revamp of auxiliary systems.

Alternatively the CO2 and H2O could be implement instead of air.

The energy consumption will increase while syngas mass flow could be the same or even lesser.

Steam-air AC Plasma Torch [10/13]

The stabilization of direct current arc is achieved

by ballast resistance thus the efficiency of power

supply system is about 50-60 %.

WHY AC?DC plasma torches usually have several time lower arc

voltage than AC plasma torches and thus to achieve

have the same power they have to increase current.

Arc current directly

afflict electrode

erosion.

AC power supply system suppress arc instabilities by current-limiting inductors

and a capacitive reactive power compensators (efficiency is about 98-99 %).

Due to high

stabilization

capabilities of AC

power supply system

arc could have higher

length and with higher

variation of length .

Plasma torch

Power

supply

The arc length is

stabilized by gas flow

and is depended on

gas composition.

Gas Composition Influence on Plasma Torch Power [11/13]

Current = 28.12-29.27 A

Voltage = 1.03-1.58 kV

Efficiency = 94.3-95.3 %

Steam + Air = 6.55-6.80 g/s Coulomb scattering defines arc

conductivity at temperatures

higher than ~9000 K.

The higher hydrogen content in plasma forming gas

leads to higher thermal conductivity, higher energy

losses and higher thermal capacity of plasma.

The increase of hydrogen

content in plasma forming

gas leads to decrease in

arc temperature and

consequently decrease of

arc conductivity. At a

constant current this leads

to increase of voltage drop

to sustain the current.

Arc diameter ~4.47 mm

Arc length ~798 mm

Arc diameter and length are weakly

depend on the steam/air flow-rate ratio.

Coulomb cross-

sections are on

2-3 orders higher

than elastic.

Steam Plasma Torch Power Applications [12/13]

Apart from gasification steam plasma torch could be

implemented for methane conversion, tar reforming, ash

melting and other processes demanding high energy input.

Stoichiometric plasma conversion of methane.

Estimate for constant thermal energy flux ~1 MW/m3.

3

Energy consumption on CO

conversion to H2 was neglected.

Conclusions [13/13]

Process temperature is not limited anymore by adiabatic flame

temperature. It is now possible to produce syngas almost

completely free from CO2, N2, H2O and tars.

Plasma technologies provide a

brand-new way to control

gasification process.

THANK YOU.

Additional H2+CO in syngas carry 1.5-1.7 more energy than was

consumed on their generation thus if high efficiency combined

cycle is used then net efficiency grows. Additional gains surpass

expenses ~2 times for liquid fuels production using plasma.

Electrical energy spent on plasma

formation is recovered with surplus or

transformed to more valuable energy.

Plasma process shows ~1000 °C on the gasifier wall at 77 cm

distance downstream from plasma injection zone.High temperature zone is limited and

consequently gasification rate is high.

The higher enthalpy the more energy is transformed to syngas

LHV and higher temperature in injection zone.Plasma process parameters are enhanced

with increase of plasma enthalpy.

Highest plasma energy content was ~12 MJ/kg for steam-air operation and up to

~20 in multi-gas regime while efficiency was ~95 %, power ~50-120 kW.

Plasma enthalpy of about 20 MJ/kg of H2O is optimal for methane conversion at

stoichiometric regime.

New plasma torch has

high enough enthalpy to

consider it for industrial

applications.