EP1985687A1

EP1985687A1 - Process and installation of thermal energy production, using a crude glycerine as fuel in a boiler

Info

Publication number: EP1985687A1
Application number: EP07425235A
Authority: EP
Inventors: Paolo Lucarno; Giorgio Mazzanti
Original assignee: Energy Biosystem Srl
Current assignee: Energy Biosystem Srl
Priority date: 2007-04-20
Filing date: 2007-04-20
Publication date: 2008-10-29

Abstract

In a process of thermal energy production using a crude glycerine as fuel in a boiler, the saline components are separated continuously from the other products of combustion of the crude glycerine at the same time as the processes of thermal exchanges take place in the boiler. The installation to implement the process comprises a boiler, said boiler comprising at least
- a burner,
- a furnace,
- a convector, and
-an exit filter,
and the burner is fit with a surrounding muffle conformed so that the saline components are swept downstream in the gases of combustion without depositing on the burner.

Description

Biodiesel production worldwide has been growing tremendously over the past several years. The principal by-product of this production is glycerol, also known as glycerine. It occurs in vegetable oils at the level of approximately 10% by weight.
In the transesterification process, oils and/or fats, rich in triglycerides are mixed with an alcohol, such as methanol and a base such as potassium or sodium hydroxide, resulting in a methyl ester biodiesel stream and a glycerine side-stream. This glycerine side-stream contains a mixture of at least 60 % glycerol (typically 85-92%), methanol, water, inorganic salts (2-10%), free fatty acids, unreacted glycerides, methyl esters and a variety of other organic matter (typically 1-4%). The methanol may be stripped from the stream and reused, leaving behind, after neutralisation, what is known as crude glycerine. In the following text, the term crude glycerine will thus designate a mixture containing a minimum quantity of 60 % of glycerol, between 2-10 % inorganic salts, and a variety of organic matter, which may include free fatty acids, mono-, di, and triglycerides, methyl esters, methanol and water. In this raw form, crude glycerine has a high salt and free fatty acid content and substantial colour (yellow to dark brown). Consequently, crude glycerine has few direct uses due to the presence of the salt and other species, and its fuel value is also very low.
As the demand and production of biodiesel grows, the quantity of crude glycerine generated grows paralelly, and its utilisation becomes an urgent topic.
Refining of the crude glycerine depends on the economy of production scale, and/or the availability of a glycerine purification facility. Larger scale biodiesel producers refine their crude glycerine and move it to markets in the food, pharmaceutical and cosmetic industries. It is generally treated and refined through filtration, chemical additions and fractional vacuum distillation to yield the various commercial grades such as dynamite grade, yellow distilled grade, and chemically pure grade. It can also be refined by less energy intensive methods of filtration, through a series of ion exchange resins. Small to moderate scale producers who cannot justify the high cost of purification find crude glycerine utilisation or disposal to be a problem.
It has been proposed to use crude glycerine as a fuel, since glycerol has a calorific power of about 4200 Kcal/kg, for producing thermal energy or vapour, but all attempts failed, due to the high salt content of crude glycerine. Indeed, all attempts to fire crude glycerine either alone or in admixture to other fuels in furnaces, boilers or engines resulted in obstruction of burners and other vital parts, and blockage of the installations, due to settling and fur concretions of a fine powder of potassium and / or sodium carbonate, the formation of such a powder being unavoidable upon firing crude glycerine.
The aim of the present invention is to overcome the above problem. This aim is achieved by a process, according to process claim 1, and by an installation, according to installation claim 8.
According to the invention, in a process of thermal energy production, using a crude glycerine as fuel, the saline components are separated continuously from the other products of combustion of the crude glycerine at the same time as the processes of thermal exchanges take place in the boiler.
The installation to implement this process comprises a boiler, said boiler comprising at least

a burner,
a furnace,
a convector, and
an exit filter,

Thus, the process according to the invention results in producing heat and/or steam by means of the thermal exchanges of the main stream of combustion gases with coolant fluids and in producing a side-stream of alkaline carbonate powder. Disposal or reuse of such a carbonate powder by-product does not present any problem.
Surprisingly, it has been found that despite the various origins of the vegetal oils, colza, soybean, rape, palm, etc. processed for producing biodiesel, and the process variants producing biodiesel and crude glycerines as by-product, firing of crude glycerine at high temperature always produces alkaline carbonate, mainly sodium carbonate, in the presence of the CO2 of the combustion gases. This sodium carbonate solidifies when the gas temperature falls below 670° K., leading to a powder with a substantially constant granulometry, wherein about 70% has a particle size in the range 1-60 µm and about 30% is coarser. It is thus possible to design a plant, including a boiler for firing crude glycerine, whose conception does not depend from the specific origin and composition of the crude glycerine.
In such a boiler, a major part of the saline components, i.e. carbonate, is solidified by heat transfer upon contact of the products of combustion with thermal exchanging means of the boiler and set down at the bottom of the compartments of the boiler that shelter the thermal exchanging means.
A part of the saline components which is depositing on the thermal exchanging means is detached there from by means of vibrations, so as to deposit at the bottom of the compartments, and taken off there from by transport means. The saline components which are not set down at bottoms of compartments are carried to and retained by filter means arranged downstream the boiler.
Other features and advantages of the present invention will appear to those skilled in the art from the following description of an embodiment of an installation, in relation to the drawings, wherein

figure 1 is a schematic horizontal sectional view of an embodiment of the installation;
figure 2 is a schematic front view of the same installation, with a partial cut out illustrating exchanging means.

As shown by figure 1, the installation, generally designated by 1, comprises a burner 2, which is fed with crude glycerine and air under pressure. The crude glycerine is brought to the burner of the boiler at a temperature above its temperature of inflammability and lower than the temperature of acrolein formation. Thus, the crude glycerine is preheated to a temperature comprised between 140° C. and 170° C.
The exit nozzle 3 of the burner is designed to mechanically atomise the glycerine/air mixture and to expel it horizontally. This part of the burner is fit with a horizontal cylindrical surrounding muffle 4 with inner walls made of refractory material, conformed so that the saline components are swept along by the gases of combustion without depositing on the burner or on the inner walls of the muffle. Thereto the dimensions of the muffle are calculated so that the exit temperature of the combustion gases leaving the muffle are of between 1300 and 1700° C, in particular about 1550-1650°C, which is much higher than the melting temperature of sodium carbonate.
Leaving the muffle, the combustion gases enter a furnace 5, which may comprise one or several compartments, depending on the overall size of the installation 1. The inner walls of the furnace are constituted of refractory materials.
These one or several compartments of the furnace 5 are equipped with steel tubes 6 for the circulation of a fluid coolant, arranged along the inner walls of the compartments, recovering radiating heat from the flow of combustion gases. The tubes 6 inside the furnace are suspended and arranged substantially straight up on a major part of their length, and are provided with a hammer actuated vibrator system permitting to strike and vibrate the tubes 6, for detaching alkaline carbonate which may deposit thereon. Further heat exchanger tube portions 13 may be arranged within the refractory walls.
Leaving the furnace, the combustion gases enter a convector 7. The convector has a substantially rectangular housing and may comprise one or several compartments, depending on the overall size of the installation. The inner walls of the convector are constituted of refractory material.
The convector is fit with a system of steel tubes 8 for the circulation of a fluid coolant, which are arranged in groups and transversely to the flow direction of the combustion gases. The tubes 8 of the convector are suspended and arranged substantially straight up on a major part of their length and are provided with a hammer actuated vibrator system permitting to vibrate the tubes of the convector for detaching sodium carbonate, that accumulates thereon.
The boiler shown in figure 1 comprises an economizer 9 downstream of the convector and upstream of the exit filter for enhancing the energy recovering rate. The construction of the economizer is similar to the construction of the convector: the economizer comprises a system of steel tubes 15 for the circulation of a fluid.
The tubes of the economizer are suspended and arranged substantially straight up on a major part of their length and are provided with a hammer actuated vibrator system to vibrate the tubes of the economizer.
In relatively small installations, the economizer may be omitted, whereby diminishing the construction costs. In larger installations, the fluid coolants circulating in the tubes 6, 8 of the convector and the furnace are chosen among oils boiling at high temperature, the recovery of energy being achieved by the elevation of the temperature of the oil, and the circulating fluid in the tubes of the economizer is pressurized water, for the production of vapour.
Downstream of the economizer, there is a filtration unit 10. The filtration unit is comprised of two compartments mounted parallel, each of them housing a bag filter system 16 whose construction is known in the art and whose filtrating surface is sufficient for filtering the cooled down combustion gases and smoke, and for retaining the remaining solid particles of alkaline carbonate. The two compartments are alternately emptied and cleaned.
Downstream of the filtration unit is a blower 11, which takes up the gas exiting the filtration unit, and which sends the same into an outlet chimney 12.
The bottoms of the compartments of the furnace 5, the convector 7, the economizer 9 and the filtration unit 10 are equipped with hoppers 14. The accumulating carbonate powder is periodically taken off and transported away by well-known conveyor systems, for example an Archimedean screw.
Those skilled in the art will observe that the thermal conditions within the various compartments of the boiler are different in the starting phase, the stationary operative phase and the stopping phase.
In the starting phase, when the installation is still cold, it is important to avoid any deposit of carbonate on the burner. The design of the muffle provides for a high speed of the burning gas mixture and a high temperature inside the muffle even in this transient phase. Nevertheless, the temperature in the furnace in this phase is still not very elevated, and until it exceeds 670° K., the major part of the carbonate deposits in the furnace. With increasing temperature, more and more carbonate deposits within the following successive compartments of the convector, and thereafter of the economizer.
In the stationary operative phase, no carbonate deposits in the furnace, typically about 20% of the total carbonate deposits on and under the groups of tubes of the convector, and about 60% sets in the economizer. The remaining about 20% are entrained by the fumes and captured by the bag filters of the filtration unit.
Those skilled in the art will easily understand that these percentages may vary, depending upon the settings of the burner, the temperature of the burning gases, and the geometry of a specific installation. Those skilled in the art will also understand that upon adhesion of carbonate on the walls of heat exchanging tubes, the thermal conductivity of the latter diminishes, deteriorating the operative conditions of the heat exchanges. Therefore, the systems of striking hammers, upon vibrating the tubes, detaches such building up carbonate layers from the tube walls, restoring the set conditions.

Example

A glycerine firing boiler comprises:

downstream of the muffle, two furnace compartments, equipped with heat exchanger steel tubes of 60 mm diameter, providing a heat exchange surface of about 25 sq. m;
a third furnace compartment, equipped with heat exchanger tubes of 60 mm diameter, providing a heat exchange surface of 60 sq. m;
a first convector compartment, equipped with 160 vertical heat exchanger tubes of 40 mm diameter, providing a heat exchange surface of 98 sq. m.;
a second convector compartment equipped with 160 vertical tubes of 40 mm diameter, providing a heat exchange surface of 88 sq. m;
an economizer compartment, equipped with 420 steel tubes of 40 mm diameter offering a heat exchange surface of 278 sq. m;

The furnace and convector heat exchange systems are fed with oil of the type Santotherm 66. The heat exchange system of the economizer is fed with about 13'000 kg/hour water at 100° C. under a pressure of 19 bar.
The burner is fed with 1800 kg/hour crude glycerine and 12'500 kg/hour air.
In the stationary, operative phase, upon burning, the mixture produces about 13'900 kg/hour combustion gases at 1635° C. The combustion reactions are substantially complete, due to the oxygen excess imput.
The gases enter the first furnace compartment at a speed of about 2.2 m/second. The gases leave the second furnace compartment at a temperature of about 880° C., whereas the temperature of the coolant oil increases from 268 to 297° C., thereby recovering about 3420 MCal / hour. The combustion gases leave the third furnace compartment at 689° C., whereas the temperature of the coolant oil increases from 261 to 268° C., recovering about 810 MCal / hour
The combustion gases enter the first convector at 689° C. and leave it at 481°C.whereas the coolant oil temperature increases from 254 to 261°C. The combustion gases leave the second convector compartment at 372° C., whereas the coolant oil temperature increases from 250° C. to 254°C. The energy recovery in the convector is of about 1260 MCal / hour.
The gases enter the economizer at 372° C. and leave the economizer and the chimney at 153° C. The temperature of the water increases from 100°C to 160° C.
The global energy efficiency of the installation, including heat recovery through the coolant oil and through the overheated water is of about 90%.

Claims

Process of thermal energy production using a crude glycerine as fuel in a boiler, characterized in that the saline components are separated continuously from the other products of combustion of the crude glycerine at the same time as the processes of thermal exchanges take place in the boiler.
Process according to claim 1, producing heat and steam simultaneously.
Process according to one of claims 1 or 2, characterized in that a major part of the saline components is solidified by heat transfer upon contact of the products of combustion with thermal exchanging means of the boiler and set down at the bottom of the compartments of the boiler that shelter the thermal exchanging means.
Process according to claim 3, characterized in that a part of the saline components is depositing on the thermal exchanging means and is detached there from by means of vibrations, so as to deposit at the bottom of the compartments, and taken off there from by transport means.
Process according to one of claims 3 or 4, characterized in that the saline components not set down at bottoms of compartments are carried to and retained by filter means arranged downstream the boiler.
Process according to one of claims 1-5, characterized in that the crude glycerine is brought to the burner of the boiler at a temperature above its temperature of inflammability and lower than the temperature of acrolein formation.
Process according to claim 6, characterized in that the crude glycerine is preheated to a temperature comprised between 140°C. and 170° C.
Installation to implement a process according to one of the preceding claims, comprising a boiler, said boiler comprising at least
- a burner,

- a furnace,

- a convector, and

- an exit filter,
characterized in that the burner is fit with a surrounding muffle conformed so that the saline components are driven in the gases of combustion without depositing on the burner.
Installation according to claim 8, characterised in that the muffle is conformed so that the products of combustion leave the burner compartment at a temperature of between 1300° C. and 1700° C, in particular of about 1500° C..
Installation according to claim 8 or 9, the furnace of the boiler comprising one or several compartments, characterized in that the one or several compartments of the furnace are equipped with tubes along the inner walls for the circulation of a fluid coolant, in that the tubes of the furnace are suspended and arranged substantially straight up on a major part of their length and are provided with vibrator means permitting to vibrate the tubes of the furnace.
Installation according to one of claims 8 to 10, characterized in that the convector is fit with a system of tubes for the circulation of a fluid coolant, that the tubes of the convector are suspended and arranged substantially transversely and straight up on a major part of their length and are provided with vibrator means permitting to vibrate the tubes of the convector.
Installation according to anyone of claims 8 to 11, characterized in that the inner walls of the furnace and of the convector are constituted of refractory materials.
Installation according to one of claims 8 to 12, characterized in that the boiler comprises an economizer downstream the convector and upstream of the exit filter, that the economizer comprises a system of tubes for the circulation of a fluid, that the tubes of the economizer are suspended and arranged substantially straight up on a major part of their length and are provided with vibrator means to vibrate the tubes of the economizer.
Installation according to anyone of claims 10 to 13, characterized in what the vibrator means comprise a system of striking hammers.
Installation according to anyone of claims 10 to 14, characterised in that the bottoms of compartments are equipped with hoppers.
Installation according to one of claims 10 to 15, characterized in that the fluid coolants circulating in the tubes of the convector and the furnace are chosen among oils and that the circulating fluid in the tubes of the economizer is pressurized water.
Installation according to anyone of claims 8 to 16, characterized in that it comprises a blower downstream of the exit filter, and a chimney downstream of the blower.