Int. J. Hydrogen Energy, Vol. 8, No. 11/12, pp. 929-930, 1983. Printed in Great Britain.

0360-3199/83 $3.00 + 0.00 Pergamon Press Ltd.

~) 1983 International Association for Hydrogen Energy.

COMBUSTION TECHNOLOGY OF OIL MIXED WITH H Y D R O G E N P R O D U C E D FROM WATER IN SITU

T. OHTA and S. KIYOHARA*

Hydrogen Energy Research Laboratories, Yokohama National University, Yokohama, Japan, *Oriental Terminal Products Inc., Yokohama, Japan

(Received 10 March 1983)

Abstract--Two methods have been developed which can burn oil in the presence of water. The first method burns hydrogen. The hydrogen can be produced from water by d.c. electrical energy generated by a thermoelectric device composed of multistage semiconductor thermocouples attached to the side wall of a conventional oil burner. The second method reforms oil with a high temperature water vapour jet. The generated hydrogen is burnt in situ with the residual oil vapor. Combustion with water has two merits: (1) the combustion temperature becomes higher resulting in a higher efficiency of the heat exchanger, and (2) near perfect combustion of oil can be achieved minimizing soot.

U T I L I Z A T I O N OF H Y D R O G E N FORMED BY W A T E R SPLITTING DUE TO THE WASTE

H E A T OF AN OIL BURNER

A thermoelectric device composed of multistage p- (BiTe-Sb) and n-(BiTe-Se) semiconductor junctions is attached to the side walls of a conventional oil burner. Thermal energy needed to heat the p-n junction is provided by the waste heat from the burner. A water stream flows over the low temperature side of the thermoelectric device cooling it. The resulting thermal gradient is used to effectively generate electric power. Another role of this water stream is to increase the temperature of the water supplied to the electrolyzer. The efficiency of the electrolyzer increases as the sup- plied water temperature increases. The hydrogen and oxygen produced by the electrolyzer are fed to the oil burner. The hydrogen and oxygen are then burnt in the presence of the oil vapour in situ. The overall efficiency of this system, e, i.e. the efficiency of the wast heat utilization, is given by

nqo e = ~ + ew(1 - ete) (1)

where n is the nolar number of the produced hydrogen, q0 is the heat of combustion (HHV) per mole of hydro- gen, Q0 is the total heat transferred to the water decom- position system, & is the efficiency of the water heating process, and ere is the efficiency of the thermoelectric conversion process. The term on the right-hand side of equation (1) is the hydrogen production efficiency from water vapor to high temperature and high pressure water (or saturated vapor). The second term is the efficiency of making the water vapor. The heat that is transferred from the burner side wall to the thermo- electric device generates electric energy with an effi- ciency less than 5% usually. This was also true in pre- liminary experiments. However, the waste heat from the thermoelectric device is used to heat the cooling

water for the device used to produce the high temper- ature water (vapor). This vapor is fed to the electrolyzer and decomposed to hydrogen and oxygen at high effi- ciencies. About 70% of the waste heat from the burner can be recovered as hydrogen fuel. The biggest problem in this system is to develop the thermoelectric materials which can sustain temperatures of 700°C and above. Some thermoelectric materials, such as Ge-Si alloys that have been utilized in the Voyager Spacecraft are better than B i T e systems, but stable solder for high temperature are not known yet (Japanese patent pending).

BURNING OF H Y D R O G E N P R O D U C E D BY STEAM R E F O R M I N G OF OIL

Hydrogen production is generally done today by steam reforming of petroleum in the following way: (m)

CnH,~+nH20+AQo---~nCO+ n + ~ - Hz, (2)

and CO + H20 --* CO2 + H2 + 10 kcal/mol. (3)

In a country such as the U.S.A. where natural gas is abundant, the petroleum is replaced by natural gas (CI-L). In this case of steam reforming of methane, the heat required for the reaction is AQ0 = 49.39 kcal/mol. However, in Japan, almost all of the petroleum is imported and hydrogen is produced by the steam reforming of Naphtha. If water mist is made by some way such as the centrifugal jet device or pump jet device and is exhausted into a high temperature (700-9000C) oil vapor and the reaction is given the equations (2) and (3). This hydrogen is burnt in situ with the petroleum vapor.

Conventinal direct combustion of petroleum is described by the following equation:

CnHm+(n+m/4)O2--~nCO2+2H20+AQ1. (4)

929

930

On the other hand, the combustion of hydrogen fuel is expressed by the next equation:

+ 2 H20 +

T. OHTA AND S. KIYOHARA

Suitable metals are limited to titanium, titanium alloys and stainless steels. This limitation can be seen from an examination of the following chemical reaction:

M + H20 --o H2 + MO, (7)

(5) where M is the metal quasi-catalyst. The authors of this paper have observed that these metals and alloys can be oxidized by high temperature water vapor as described by equation (7). It is obvious the heat output can not be increased by the water vapor mixing. How- ever, three important merits can be listed as follows:

(1) The temperature increases due to the hydrogen-oxygen combustion. This increases the effi- ciency of the heat exchanger which is proportional to the gradient of the temperature.

(2) Improved combustion is realized because the pet- roleum fuel decomposes into many species of molecules with decreased molecular weight which in turn can be oxidized easier. Also the higher temperature of com- bustion yields improved combustion.

(3) No soot is observed in the combustion vessel for the present cases. This is due partly to the complete combustion of the fuel. A blue or nearly colorless flame is observed with no trace of a clear yellow or orange color. This is the result of the aggregation of petroleum molecules or of the carbon-rich particles being decom- posed by steam reforming and the produced fuel burning to evolve carbon dioxide and water only.

The hydrogen energy system is based on the tech- nology of water splitting which is innovative and needs to be realized. Nevertheless, this system could solve a difficult problem of hydrogen transport and storage. From this point of view, one must recognize the import- ance of the combustion technology of oil mixtures with water in situ.

where the hydrogen fuel can be provided by the steam reforming of petroleum given by equations (2) and (3), i.e.

CnHm + 2nH20 + AQ0---~ nCO2

+ m H + + ( 2 n ~ - ) 2 10nkcal/mol. (6)

The balance of heat output between the above two can be evaluated by the comparison between AQ1, the output of the conventional oil combustion, and AQ2 - AQ0 + 10n, the output of the present combus- tion system. The thermal energy output of our present case is obviously less than or equal to that of the direct combustion case.

DISCUSSION

A well-known method for the combustion of a water-petroleum mixture is the emulsion method. Among other things the water-in-oil method has flour- ished studies to reduce NOX products, since the tem- perature of the emulsion combustion is lowered. Another study of the water-in-oil mixture method of combustion is the use of a metal to intervene as a quasi-catalyst. If a high temperature water vapor jet (600°C and above) is impinged on a metal surface and deflected into an oil flame, then the water vapor burns.