(56d) Non-Conventional Methods of Obtaining Combustible Liquid Fuels

Introduction

Limited world reserves of liquid
fuel as well as the general trend to reduce atmospheric contamination pose many challenges for
producers of heat
energy. These challenges include increasing fuel combustion efficiency and at
the same time reducing emissions. Solution to these problems resides in continuously improving
the design of burners and the technology of liquid fuel combustion.

Review of recent studies and publications.

The most promising method of atomizing liquid fuel is using dedicated nozzle cavitators
that ensure continuity disruption and improve the dispersion of liquid fuel [1]. Cavitation bubbles and cavity pockets are
formed in sites where fluid pressure is lower than the critical one [2, 3 and 4].

Objective.

The theoretical investigations of processes in cavitation nozzles are based on mathematical modelling of fluid flow in intricate
channels. The numerical solutions were found using the R-functions method
[9]. Different channel flow conditions were investigated with the POLE software package developed under supervision of
the late Academician V.L. Rvachev in the Department for Applied Mathematics and
Computational
Methods [6] in our laboratory. In the Pole software system the R-function
method with variation methods (Ritz method, Bubnov-Galerkin method, least squares method) are used for
boundary value problems solving. Flow patterns in intricate channels were
obtained using the POLE software (Fig. 1.) [6].

 

Fig. 1. Flow functions in
channels

Designs of cavitation devices were
obtained based on investigations (Fig. 2.).

Fig. 2. Cavitation
nozzle model

Figure 3 depicts the cavitation nozzle. 
The flowing part of the nozzle is an axisymmetric channel whose inlet
has convergent tube
2 and 4, and the outlet has diffuser 5. The toroidal vortex-mixing chamber 6 is
located in the midsection of the channel (Fig. 3). Because rarefaction occurs in chamber 6 during fluid
flow in the channel, the second fuel component is sucked in via ejection orifices 8 from
auxiliary annular chamber 7. Ejection channels 8 communicate with the rarefaction zone of
toroidal chamber 6. The ejected flow sucked in from chamber 7, is
separated into m individual orthogonal flows. Each of the m flows is subject to
torsion moments created by the shape of the ejection orifices. The number m
of ejection channels, and their shape and location in the construction is
defined with a technique developed by the authors [5].

In the diffuser channel, cavitation proceeds further;
the combustion mixture film is broken up into droplets and water is dissociated partially into
Н⁺ and ОН - ions supporting the molecular
dispersion-based reactions of hydrolysis and hydrogenation of high-molecular
fractions of organic energy carriers.

During cavitation treatment, the amount of free hydroxyl groups
ОН^- in water increases,
and water acidity can increase to the ultimate value of рН = 14.0.
During cavitation,
collapsing cavitation bubbles yield important effects.  These effects include: significant viscosity reduction; surface energy
and tension change; inner energy decrease; the temperatures in the local collapse
point rise to critical values of 374 К, at which the latent vaporization heat is practically
absent; the water structure changes; intermolecular bond energy is released; water
luminescence is observed; electric conductance increases, and chemical activity
increases. The chemical compounds in water are activated, since there is practically no pure water, and
in the natural state water is a solution of inert gases and different microelements.
Reducing the heat of vaporization of cavitated water yields dramatic energy saving, since the heat
of vaporization restores its prior value with subsequent condensation of the vapor obtained.
The same pertains to reducing surface tension viscosity. This decreases the work expended on
formation of vapor bubbles and their subsequent growth [5].

Fig. 3. Cavitation nozzle

Experimental Results

.  For
cavitation treatment we can use black oil, water,
unconditioned hydrocarbons, refinery and coal industry wastes, tank washes,
biomass and others.

Three samples of nozzles were used for testing. They were made to the
above-described techniques
(Fig. 4). The small-size nozzle ? inner
diameter of the toroidal chamber ? 30 mm (external
size is ≈3,5 cm in diameter).  The
medium-size nozzle ? inner diameter of the toroidal chamber ? 40 mm (external size is ≈5 cm in diameter).  The large-size nozzle ? inner diameter of the
toroidal chamber ? 50 mm
(external size is ≈7 cm in
diameter).

                                                          
Fig. 4. External view of tested nozzles

Tests were conducted on a certified instrumentation and monitoring gas
test bench.
Compressed air from the mains was fed to the nozzles, and the atomized liquid was standard automobile diesel
fuel.

The tests yielded the
following results:

1.When scavenging the nozzles without feeding fuel it was found that,
in the investigated
air pressure range, there was rarefaction in the fuel channel. Its value increased with growth of initial
air pressure at the nozzle inlet (Figs. 5 and 6).

2.Stable atomizing starts at pressures of about (0.3 ? 0.5) kgf/cm².

3.During fuel atomizing two major fractions were distinguished, including,
the fine fraction
with particle sizes of 5 µm to 10 µm, and a large fraction with particle sizes close to 100 µm. The fine
fraction fills the central part of the atomized stream, practically without voids. The large
fraction is distributed over the stream periphery and it is made up of droplets
formed during disintegration of the film of the liquid phase, which flows with low velocity
over the walls of the nozzle outlet port and disintegrates under action of the inner
part of the stream flowing out with high velocity.

Fig. 5. Rarefaction
in the fuel channel vs. nozzle inlet air pressure

1 ? small-size nozzle;
2 ? medium-size nozzle; 3 ? large-size nozzle;

P_inlet ? air pressure in inlet of the nozzles; P_t ? pressure in toroidal vortex mixing chamber

Fig. 6. Air flow
rate vs. Nozzle inlet air pressure: ? small-size nozzle;

2 ? medium-size fornozzle; 3 ? large-size nozzle;

P_inlet ? air pressure in inlet of the nozzles; G ?
air volumetric flow rate

To
measure the size of the droplets we use the conductometric
method and the laser method. The conductometric
method is the better method  to measure the
size of the droplets in local zones, but the laser method is better for
integral measurements.

 

Figure 7. Investigation of spraying dispersion using
the laser method

The first run of
experiments was conducted as follows: of the 100 % of
a mixture
of roughly 15 liters, 20 % accounted for black oil and 80 % was virgin petrol. Water in the
amount of 25 % of that of black oil was added to the mixture. Batch refinement was
conducted upon reaching the temperature of 80 ºС, and the mixture density
was 0.837175 kg/m³. The experimental data are given in Table 1.

Table 1.
Experimental results of thermal draw refinement of the treated mixture

I.c.	93 ºС
10 %	120 ºС
20 %	137 ºС
30 %	154 ºС
40 %	175 ºС
50 %	209 ºС
60 %	251 ºС
70 %	314 ºС
80 %	335 ºС
90 %	320 ºС
F.c.	341 ºС
Yield	94 %
Residue	5 %
Losses	1 %
Temperature in closed crucible ? 14 ºС

The results
indicate practically complete batch refinements of black oil in a virgin petrol environment, yielding, mainly,
the petrol draw and diesel fuel.

The second run of
experiments (Table 2) was refinement of black oil in a diesel fuel environment with a 20 %
addition of virgin petrol.

Table 2. Experimental results of
draw refinement

Washout after refinement	Initial
I.c. 53 ºС	I.C. 91 ºС
10 % 79 ºС	10 % 114 ºС
20 % 95 ºС	20 % 131 ºС
30 % 108 ºС	30 % 149 ºС
40 % 131 ºС	40 % 166 ºС
50 % 187 ºС	50 % 214 ºС
60 % 266 ºС	60 % 278 ºС
70 % 330 ºС	70 % 295 ºС
82 % 358 ºС	82 % 294 ºС (initiation of coking)
F.c. 358 ºС	Ρ204=0.7550 g/cm3
Yield 90 %	Flash temperature in closed crucible ? 18 ºС
ρ=0.763 g/cm3	Water ? 0.018 %
Flash temperature in closed crucible ? 22.5 ºС

In spite of
refining black oil mainly in diesel fuel, more than 25 % of the black oil
passed to the distillate draw from the initial 35 % of black oil.

This
set up was also used to study ACLF, comprising the bio mud with a moisture content of
80 % and grade M100 black oil. The fuel obtained was combusted in a firing test
bench, including the developed nozzles [9]. The investigations demonstrate that the
ACLF (20 % of bio mud and 80 % of M100 black oil) is close in fuel
quality to M100 black oil.

                                                         Fig. 8. Firing
ACLF with a nozzle

Conclusions.

The studies conducted have shown that to create and effectively combust liquid fuel new fluid
cavitation technologies are required. It is necessary to use nozzles-cavitators as atomizers
during combustion. They do not require special conditions, i.e. heating. It was shown
that, by achieving conditions of well-developed bubble cavitation, it is possible to improve
atomizing quality and significantly change the chemical composition of combusted fuel mixtures.