THE EXTRACTED OLIVE POMACE FOR FUEL

THE EXTRACTED OLIVE POMACE (olive pits) FOR FUEL

Utilization of biomass the extracted pomace olive

Aristides Strofylas

Mechanical - Electrical Engineer

School of Engineering, University of Patras Greece

Member TEE - AM 36818

1. Origin of the biomass of olive pits ( extracted olive pomace )

The olive pomace core is produced in miller (oil mills) processing of olives (olives) for receiving the olive oil. Removal of olive oil, the vast majority of mills, made by centrifugation in a centrifugal separators two or three phases. The two-phase separator produces olive pomace humidity 64% - 68%, while the three-phase olive pomace humidity 48% - 54%. In both cases the olive pomace still contains olive oil the range 8% - 12% (dry) not received by centrifugation.

Then the olive pomace is transferred to factory (olive pomace) to make delivery of the residual oil (crude olive-pomace oil ) with the method of extraction with hexane

The factory is the drying of olive pomace that the humidity to fall to 8% - 10%. The drying is done in drying cylinders (rotary) where with the help of metal fins "rocked" and comes in direct contact with hot air stream generated by the mixing of a gas fireplace burning olive pits with ambient air.

Then in sections of olive pomace extraction is the extraction of dry olive pomace longer to gain the olive oil pomace. Usually used semi-system (static percolators (extractor) and continuous distillation system) and liquid extraction (solvent) is used pure hexane. The solvent is fed into the percolators and blend olive pomace oil - solvent (michella) resulting in a continuous distillation driven complex where the solvent is distilled attributed in gas form, and olive pomace oil-free solvent.

After removal of hexane - solvent by percolators remains in him dry - extracted olive pomace (olive pits) which is removed by means of steam under low pressure.

2. Properties - olive pits ( extracted olive pomace )

2.a. Composition and characteristics

The olive pits consist of:

• from the olive stones is woody and fragmented

• from the mesocarp (olive paste) - pulp of olive (dried) powder form

• and from the skin of olive also in powder form

Drawing on existing analyzes of the woody part is about 55% of its weight, while the remaining 45% is the powder (pulp and skin). Also should mention that there is an olive pomace oil rate of about 0.5% to 1.2% (dry weight), which were received during the manufacturing process of extracting and remains as residue oil in olive pits.

The specific gravity of the "bulk" olive pits ranges from 720 - 750 Kgr / m3 and humidity usually from 12% - 15%, while the experience has shown that the upper limit of moisture for satisfactory combustion is 18%.

The composition of the olive pits as it is about the same as that of wood and in accordance with existing analyzes (NTUA 1981 and NTUA 2000) is as follows:

• Carbon (C) : 49,7% - 50,1%

• Hydrogen (H) : 6,0% - 7,0%

• Nitrogen (N) : 1,1% - 1,6%

• Sulfur (S) : negligible (0.01% -0.08%)

• Oxygen (O) : 38,1% - 38,8%

From an environmental perspective is very important to very low to negligible content of sulfur and that the fuel contains no toxic compounds or heavy metals. Also very important both operationally and from an environmental perspective (particulate emissions), is that the ash is about 3.5% - 4.5%.

As disadvantages can be mentioned:

• The smell - odor of stored olive pits (long enough) due to the fermentations carried out in the fleshy part (pulp) and emerge during the scraping of the material (loading, emptying, transportation provisions)

• The risk of ignition, especially when stored in piles high altitude due to the temperature that develops inside, again because of pulp fermentations. (But must be remembered that the flame is generated after 1-2 days warning of the appearance of the disguised smoke point)

• The difficulty of the olive pets flow when it is stored in large silo (over 1 m3) and humidity is above 12%.

• The white smoke (visual disturbance) occurring during combustion which is mainly due to that portion of the olive pits moisture is eliminated in the form of vapor

It should finally be mentioned that in many units is the woody air separation from the fleshy part (pulp) of the olive pits (where it is possible to place the souls of other uses - eg animal feed) and in this case the woody part shows no from the above disadvantages.

2.b. Calorific value power – olive pits

The calorific value of fuel, from laboratory analysis is estimated at 4.700 - 5.000 Kcal / Kgr

Calorific value (dry): 5.063 Kcal / Kgr (NTUA - May 2000)

Calorific value (dry): 19,7 KJ / gr = 19.700 KJ / Kgr = 4.710 Kcal / Kgr (NTUA - May 1981)

But theoretically from the elemental analysis presented above, the calorific value (dry) show ("Fireplaces and Steamboiler" - Lefas - page 93)

8.100 * C +29.000 * (H - O/8) + 2.500*S = 4.400 - 4.650 Kcal / Kgr

The beneficial calorific value, however, is much smaller for two main reasons:

• The fuel moisture ranges from 10% - 18%

• The need to provide combustion air with an excess of up to 50% (to achieve perfect combustion) and hence the relatively large heat loss in exhaust emissions.

The beneficial calorific value calculated from the detailed tables (due to loss of moisture and gases) and for example say that olive pits for moisture 10%, with an excess of 40% of combustion air and exhaust emissions temperature to 180o C, the beneficial calorific value is 3.350 Kcal / Kgr, and olive pits corresponding to 18% moisture (and the same exhaust emissions temperature) downgraded to 2.940 Kcal / Kgr.

During the writer's opinion the price should be reflected in the general calculations is 3.100 - 3.200 Kcal / Kgr.

The thermodynamic equivalence of olive pits over other fuels is as follows (for olive pits humidity 14%, with an excess of 40% of combustion air and exhaust emissions temperature of 180o C):

• 3500 over fuel oil: 7.230 versus 3.150 Kcal / Kgr = 2,296

• over diesel: 9.460 versus 3.150 Kcal / Kgr = 3,004

• for pet coke: 6.830 versus 3.150 Kcal / Kgr = 2,167

(*) In the above equations is taken into account the loss of gas calculated at the required combustion air and is as follows:

Olive pits : air combustion with an excess of 40% - 19.5% loss of gas

3500 fuel oil : Combustion air in excess of 15% - 8.2% loss of gas

Diesel: air combustion with excess 5% - 12.8% loss of gas

Pet Coke: air combustion with excess 40% - 10.4% loss of gas

Finally we should mention that if you do of olive pits in woody and fleshy part, based on existing elemental analyzes, useful thermodynamic value calculated by the two parties (for 14% humidity, air combustion with excess 40% and exhaust gas temperature of 180o C):

• woody part (wood, olive pits): 3.440 Kcal / Kgr

• fleshy part (pulp, olive pits): 2.800 Kcal / Kgr

The combustion temperature, according to the experience and the literature, ranging from 1.200o C to 1.300o C (K. Lefas)

2.c. Required air combustion - Exhaust

From the elemental analysis of olive pits can become the theoretical calculation of the required air for combustion. The basic data is burned (C) to produce CO2 and (H) to produce H2O.

The required amount of oxygen calculated by the formula ("Fireplaces and Steamboiler” - K. Lefas - page 100)

V = (8/3)*C + 8*H - O + S Kgr / Kgr olive pits

while considering that the proportion by weight of oxygen in air is 23,2%, the volume ratio at 21,0% and that the specific gravity (0oC - 760 Torr) is 1,429, the required volume of air will be:

L = (8/3)*C + 8*H - O + S Nm3 / Kgr olive pits

1,429 x 0,21

So an air about 5.0 cubic meters (Nm3) per Kgr olive pits normally (0oC - 760 Torr).

But in practice the perfect combustion with excess air of 50% and so the amount of air required is 7,5 Nm3 per Kgr olive pits (in normal conditions).

The volumes of gas (exhaust emissions) apovalomenon calculated from the following types (normal - 0oC - 760 Torr): («Fireplaces and Steamboiler " - K. Lefas - page 103)

"Dry" exhaust

V = 8,89*C + 21,1*(H - O/8) + 3,33*S + 0,796*N = 4,21 Nm3 / Kgr olive pits

"Wet" exhaust (fuel moisture 14%)

V = 8,89*C + 21,1*(H - O/8) + 3,33*S + 0,796*N + 1,244*W = 5,04 Nm3 / Kgr plive pitsl

Deciduous exhaust (with 40% excess air)

8,75 Nm3 / Kgr olive pits

Based on elemental analysis also estimated the fuel and the percentage composition of the exhaust (noted that it is very important for the thermodynamic characteristics in the calculations yields heat exchangers "exhaust - fresh air" and steam) of perfect combustion.

Exhaust gas composition by weight of olive pits

2.d. The particle size distribution of olive pits

As discussed in the article "Issues calculation cyclonic separators - The particle size distribution of olive pits (https://sites.google.com/site/pyrhnoxylo), the particle size distribution of dry, olive pits and so is as follows:

As the chart shows the average grain diameter (d50) for material that has been grinding is just under 600 μ (about 560 μ), while the olive pits that has been grinding is over 1.200μ.

This fact combined with the fact that the ash content is around 3.5% - 4.5%, implies that the burning olive pits has no nuisance in terms of particle emissions, as long as a cyclonic separator installed at the exit of exhaust.

This is also evident from the table below showing that the average grain diameter (d50) for the olive pits collected by a cyclone fired steamboiler olive pits is below 125μ

3. Procedure and description of how combustion

The burning olive pits at various thermal units (fireplaces drying lines, notables water boilers, hot water heating boilers, etc.) is done by using special devices and olive pits supply of combustion air, which generally can be divided into the following categories:

• with metal burner, with single "metal burning vessel (usually small capacity combustion devices to 500 Kgr / h and thus performance and up to 1.500.000 Kcal / h)

• with metal – iron burner, which has cast iron combustion boats and prefabricated cast iron grate (provisions for greater combustion capacity from 500 up to 1.500 Kgr / h and thus performance and up to 4.500.000 Kcal / h)

• with "double" metal – iron burner (for even greater capacity combustion devices up to 2 X 1.500 = 3.000 Kgr / h and thus performance and up to 9.000.000 Kcal / h)

Each burner olive pits basically consists of 4 parts:

• The Silo

• the promotion of transport screw burning olive pits

• the simultaneous promotion fan air for combustion at the burning grid

• the burning grid

From experience, it is proposed the combustor in the quantity of olive pits are fed adjustable (with Inverter or pulleys), while regulating the amount of the required combustion air can be done with appropriate "damper" (if the fan is correctly calculated to burn the maximum amount of fed olive pits)

Another way of burning olive pits has been successfully applied is to promote the combustion space with "air transportation", provided that the material is "pulverized" in grinder or has applied permanent drainage system secondary combustion air across the surface area combustion.

A key point in setting and achieving optimum combustion (pure white smoke) is to maintain the "right mix of burning" (ie the mix "material burning" of the provided against "incombustible material"). This implies that during the disconnection new material should be intended to cover direct and stop the drain of combustion air.

4. Common problems in homes burning olive pits

The most common problems burning olive pits in various thermal units (line drying, water notables boilers, hot water heating boilers, etc.) are mainly due to miscalculations or technical errors in the installation of combustion system.

The most common error is "no" (small plants) or "wrong choice" (in large installations) to the suction blower exhaust, which results in progressive clogging ("blocked") of the thermal unit that normally contains the array of tubes (steam boiler or steam heat pipe heat exchanger, etc.).

The "blocked - blocking" of ash from thermal plant olive pits are much greater portion of moisture from the olive pits and in the end leads to incomplete combustion resulting in the accumulation of unburned material in the combustion chamber and the strong emergence of black smoke (CO + C).

Another common error is "no" or "wrong design" extracting the cyclone exhaust (especially in small installations for heating homes, bakeries, dairies etc.), which results in a miscarriage in the surrounding area small particles of unburned wood containing the olive pits (small charcoal).

The same problem occurs, years ago, during operation of large steam boiler (builders) in factory, which operated with natural draft (so it built tall chimneys) and without cyclonic systems.

To understand the need for the correct calculation of the exhaust fan in terms of delivery and static pressure cite the following example:

Suppose that we want to convert a thermal unit (eg steam boiler) from fuel "fuel oil" average combustion capacity 500 Kgr / h to olive pits fuel, then based on the thermodynamic equivalence of the two fuels should burn 500 X 2,296 = 1.150 Kgr / h olive pits.

The combustion of this quantity olive pits (humidity 14% - with an excess of combustion air 40%) will produce 1.150 Kgr / h x 8,75 Nm3 / Kgr = 10.000 Nm3 / h, respectively, while the exhaust from the combustion of fuel oil it was only 4.900 Nm3 / h (with 15% excess air).

So the volume of flue gas is almost double of course means a big difference in static pressure fan since the passage of heat from the unit will require much more back pressure.

5. Thermodynamic characteristics of combustion efficiency olive pits

It is necessary to comment on a misconception prevailing in the market that "climate change and fuel oil or other fuel in olive pits as a result of the degradation capacity of the corresponding thermal unit (steam boiler or heat exchanger)," which is arbitrary and not based in any analysis - scientific documentation.

It is of course given that the loss of gas when burning olive pits is higher against loss in case of fuel combustion, but this difference is incorporated in beneficial calorific value of the two fuels and thus has no effect on the thermal efficiency unit.

Also the difference in the thermodynamic characteristics of the two gas stations (resulting from different composition) is not in no way justifies the above concept.

Certainly there is a significant difference due to temperature and initial combustion enthalpy of the flue gas dual-fuel (heat transfer by radiation - convection) but on the other hand it should be noted that almost twice the output volume exhaust from burning olive pits requires greater speeds which results in a strong improvement in the rate of heat transfer due to convection. Furthermore, especially in large steam boiler requires the installation water notables which increases the thermal surface in approximately 25 m2.

In practice we have achieved steam 8.000 Kgr / h, in steam boiler heat surface 180m2 (3x exhaust path, RUSTON), ie 45 Kgr steam capacity per m2, adding double notables thermal surface 28m2.

So in conclusion "to modify and change the fuel from fuel oil to olive pits not result in degradation of the thermal capacity of the respective unit (steam boiler or heat exchanger)," but if a proper study of all aspects of installation.

6. Pollution control systems in fireplaces burning olive pits

As shown above, the main problem arising from the use of the referenced fuel, since combustion is "dot" with excess air and since the S content is negligible, is the emission of ash from burning, but is easily handled with adding a cyclone separator.

The installation of cyclone separator based on the newest concepts and calculations referred to in articles:

1. "The problem of cyclones outbreaks recycled turbulent layer" - Professor Dr. K.Ch.Lefas Mechanical weekend "Wirbelschicht-systeme" of VGB at 14 -15 / 11/1990 in Essen.

2. VDI - Warmeatlas - Version 1991 - Lj1/Lj8 - Prof.Dr. - Ing.E.Muschelknautz / Dipl. - Ing.M.Trefz - Stuttgart.)

gave excellent results.

A copy of this article, we can find at: https://sites.google.com/site/pyrhnoxylo/kyklones