U.S. patent application number 12/518524 was filed with the patent office on 2011-09-29 for integrated process and related system for obtaining energy from waste with low investments and high thermoelectric yields.
This patent application is currently assigned to ECODECO S.R.L.. Invention is credited to Cristina Donati, Gianni Donati, Giuseppe Natta.
Application Number | 20110232284 12/518524 |
Document ID | / |
Family ID | 39512149 |
Filed Date | 2011-09-29 |
United States Patent
Application |
20110232284 |
Kind Code |
A1 |
Natta; Giuseppe ; et
al. |
September 29, 2011 |
INTEGRATED PROCESS AND RELATED SYSTEM FOR OBTAINING ENERGY FROM
WASTE WITH LOW INVESTMENTS AND HIGH THERMOELECTRIC YIELDS
Abstract
A process is described for obtaining energy from waste,
comprising the following phases: a) bio-drying of municipal solid
waste (MSW) to transform it into refuse-derived fuel (RDF), a dry,
homogeneous material with piece size of around 20-30 cm, known by
the name of RDF; h) compacting of the material obtained from phase
a) into bales or BIOCUBr and storage of the BIOCUBI.RTM. in
bioreactors; c) activation by wetting with water of the bioreactors
to produce biogas by anaerobic digestion; d) combustion at the
start of the material obtained from phase a) (RDF) and subsequently
of the residue already digested in the bioreactors, and therefore
not biodegradable, in a waste combustor provided with a system of
purification of combustion gasses and production of superheated
steam at approximately 400.degree. C. and pressure of around 70
bar; e) combustion of the purified biogas in a conventional boiler
provided with re-superheaters for raising the temperature of the
steam produced by the waste combustor by approximately 100.degree.
C.; f) use of the steam produced in this way in a turbine coupled
with an alternator for the production of electrical energy. The
invention also relates to a system for the implementation of this
method.
Inventors: |
Natta; Giuseppe; (Giussago,
IT) ; Donati; Gianni; (Giussago, IT) ; Donati;
Cristina; (Giussago, IT) |
Assignee: |
ECODECO S.R.L.
Milano
IT
|
Family ID: |
39512149 |
Appl. No.: |
12/518524 |
Filed: |
December 6, 2007 |
PCT Filed: |
December 6, 2007 |
PCT NO: |
PCT/IB07/03781 |
371 Date: |
July 1, 2009 |
Current U.S.
Class: |
60/653 ; 110/223;
110/224; 110/229; 110/345; 110/346; 60/670 |
Current CPC
Class: |
F23G 5/006 20130101;
F23J 2217/10 20130101; F23G 2900/50208 20130101; F23G 2900/50209
20130101; Y02E 20/12 20130101; F23J 2219/30 20130101; F23G 5/02
20130101; F23G 2202/103 20130101; F23G 2202/30 20130101; F23G
2206/203 20130101; F23G 2201/40 20130101; F23J 2219/60 20130101;
F23G 5/04 20130101; F23G 5/46 20130101 |
Class at
Publication: |
60/653 ; 110/223;
110/224; 110/229; 110/346; 60/670; 110/345 |
International
Class: |
F01K 7/38 20060101
F01K007/38; F23G 5/02 20060101 F23G005/02; F23G 5/04 20060101
F23G005/04; F23G 5/00 20060101 F23G005/00; F23J 15/00 20060101
F23J015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 12, 2006 |
IT |
MI2006A002381 |
Claims
1. Process for obtaining electrical energy from waste, comprising
the following steps: a) bio-drying municipal solid waste (MSW) into
refuse-derived fuel (RDF), said RDF comprising a dry, homogeneous
material with piece size of around 20-30 cm; b) compacting the RDF
obtained from step a) into bales and storing the bales in
bioreactors; c) activating the bioreactors by wetting the bales
with water to produce biogas and a non-biodegradable residue
through anaerobic digestion; d) combusting the non-biodegradable
residue of step c) in a waste combustor provided with a system for
combustion gasses purification to produce superheated steam at
approximately 400.degree. C. and pressure of around 70 bar; e)
combusting the biogas in a conventional boiler equipped with
re-superheaters for raising the temperature of the steam produced
by the waste combustor by around 100.degree. C.; and f) directing
the steam produced in steps d) and/or e) in a turbine coupled with
an alternator for production of electrical energy.
2. (canceled)
3. Process according to claim 1, wherein said bio-drying of step a)
further comprises feeding the MSW in a closed space, grinding the
MSW roughly and placing the ground MSW in heaps on a floor with
holes, the MSW being divided into sectors through which a current
of air is passed, wherein aerobic digestion of putrescible part
develops heat, said heat causing evaporation of water which is
removed by the current of air.
4. Process according to claim 1, wherein said bales have a size of
around 1.times.1.times.2 m and density of around 700
kg/m.sup.3.
5. Process according to claim 1, wherein said bales are produced on
site or transported from production stations distributed in the
territory.
6. Process according to claim 1, wherein said bioreactors used in
step c) are divided into sectors forming large storage tanks,
wherein said sectors are activated by injecting water into each of
them, so as to provide a continuous production of biogas and
provide, at the end of the life of each of said sectors, continuous
availability of non-biodegradable exhausted material, wherein said
non-biodegradable exhausted material is made up of inert and
plastic.
7. Process according to claim 6, further comprising blowing or
aspirating air at the end of the life of each of said sectors so as
to eliminate part of the residual water and obtain a low content of
humidity, between 20 and 25%.
8. Process according to claim 7, further comprising using hot air
or mixtures of air/gasses from the combustion to accelerate
evaporation of the water and/or obtain low residual humidity of the
waste.
9. Process according to claim 1, wherein the biogas produced in
step c) is purified of possible residual traces of chlorinated
products by passage on active carbon beds.
10. Process according to claim 1, wherein said combustion gasses
purification system comprises a series of cyclones for abating the
substantial part of he solids conveyed, a cooling tower for
controlling the temperature, a reactor fed with lime and active,
carbons for neutralising the residual acidity and adsorption of the
micropollutants and a bag filter for retaining the fine dust before
emission at the stack.
11. Process according to claim 1, wherein the steam, expanded in
the turbine, allows a yield of the thermal cycle of around 32%.
12. System according to claim 1 further comprising: a bio-dryer for
drying and stabilizing the MSW for producing RDF, said RDF being
reactive and activatable for anaerobic digestion in bioreactors;
means for the compacting of said RDF into bales; at least one
bioreactor fed with said bales for producing biogas; a waste
combustor provided with a combustion gasses purification system and
production of superheated steam; a boiler for combustion of
purified biogas provided with re-superheaters for raising the
temperature of the steam produced by the waste combustor; a turbine
coupled with an alternator for the production of electrical
energy.
13. Process according to claim 1, wherein contaminated air is
produced at end of step a)
14. Process according to claim 13 wherein said contaminated air is
used for the combusting in step d).
15. Process according to claim 1, wherein the RDF of step a) is
combusted in step e).
Description
FIELD OF APPLICATION
[0001] The present invention relates to an integrated process of
known technologies such as the BIOCUBI.RTM. process for the
bio-drying and stabilisation of MSW, anaerobic digestion in
bioreactors for the production of biogas and incineration of the
residual fraction of the bioreactors.
[0002] The present invention discloses a new process and method,
and a related system, for integrating these technologies in order
to increase thermoelectric yields and hence with maximisation of
the production of electrical energy.
STATE OF THE ART
[0003] Municipal solid waste (MSW) from selective collection, after
having been compacted, is generally dumped in controlled landfills
with previously waterproofed bases according to the prior art
(conventional landfill).
[0004] The growing production of waste, the consequent need for
further spaces for controlled landfills and the problems of
environmental impact of traditional landfills have encouraged the
development of disposal methods as alternatives to dumping in
conventional landfills.
[0005] Among these we can mention the incineration of the original
MSW or a new technology, which is now becoming widespread in Italy
and the whole of Europe, and which consists of conversion of the
MSW into inert materials which can be compacted and dumped without
environmental impact or can easily be transported and fed for
combustion to produce electrical energy.
[0006] The patent EP 0706839 of the same Applicant shows how the
MSW can be treated by aerobic digestion of the putrescible material
with low heating value to evaporate the water and obtain a fuel
with a high heating value to be fed for combustion.
[0007] Refuse-derived fuel (RDF), which we will refer to as RDF,
can be fed into grate combustors or, refined further, can be used
in fluidised bed combustors or in cement works.
[0008] This patent also shows how, without combustion systems, said
fuel is odourless, stable and free from pathogens and, when dumped,
does not therefore have the problems of environmental impact of
conventional MSW landfills.
[0009] The patent EP 1386675 shows in detail a possible version of
the plant and of the system of control and management of the
process.
[0010] It is however known that combustion of waste and also of RDF
has technological limitations concerning the combustion yields,
caused mainly by the presence of chlorine and hence of chlorides
that are corrosive to the superheaters which advise operation with
low temperatures of the steam in the boiler and typically of around
400.degree. C., with consequent low electrical energy yields
compared to the combustion of fossil fuels and typically of around
25%.
[0011] The small scale of the local incinerators that limits the
yields and increases investments per unit of fuel burnt increases
this disadvantage.
[0012] To improve the yields, in patents EP 1382806, EP 1416223, EP
1428987 and EP 1430952 the Applicant has in turn proposed the
combination of large waste combustors with a conventional
thermoelectric plant, so as to use in the best possible way the
steam produced while maintaining the limit of 400.degree. C. on the
incinerator super heaters.
[0013] The thermoelectric yields rise in this way to around 32%
although, however, the presence of a power plant available for the
integration is required.
[0014] It was later found that the RDF, dumped in a
non-conventional landfill, if wetted thoroughly, can be activated
on demand for the production of biogas, showing very high
productivity levels compared to those of a conventional
landfill.
[0015] The patent EP 1520634 of the same Applicant gives the
results obtained directly at an unconventional landfill,
introducing the concept of bioreactor, which has already been
demonstrated on an industrial scale at the site at Corteolona (PV)
with the production of 4 MW of electrical energy using internal
combustion engines.
[0016] The patent application WO2005102547 of the same Applicant
provides an integration of the bio-drying plant for the production
of RDF and a refinement process to produce a fuel with high heating
value with the bioreactor for producing electrical energy.
[0017] This integration is partial, since said fuel has then to be
transported to a combustion plant: however a first industrial
realisation is already available at the site of Villafalleto
(CN).
[0018] It should finally be noted that, among the technologies
presented to date, the activatable bioreactor represents the most
economical solution from the point of view of investments, followed
immediately by bio-drying for producing RDF while combustion is by
far the most expensive one.
[0019] Therefore the first two technologies are immediately
available, have advantages from the point of view of environmental
impact and social acceptability and therefore represent a concrete
and easily implemented solution to the problem of waste.
[0020] The combustion of the waste can be performed subsequently
when the first two stages of treatment and storage are
completed.
DESCRIPTION OF THE INVENTION The general object of the present
invention is that of eliminating the disadvantages described above
by making available a method and a related system which allows
maximum exploitation of the energy content of the waste with
minimum investments and above all by staggering these investments
in time.
[0021] A further object is that of treating waste, transforming it
into RDF and therefore making it inert and ensuring safe storage of
the fuel produced in this way in the bioreactors.
[0022] A further object is that of making available a method for
recovering from the activatable bioreactors energy at a high level
in the form of purified biogas without chlorinated substances and
therefore such as to be used to improve the heat content level of
the steam produced by the combustion of RDF or better from the
residual fraction of the bioreactors.
[0023] An additional object is that of reducing the load of
contaminated waste at the combustor, reducing at the same time the
investments and recovering the inefficiencies of the combustor by
means of the purified biogas.
[0024] These objects, and others that are to be described in
greater detail herein below, are achieved by a method and by a
process, which considers the entire life cycle of the waste and
integrates the available technologies synergically.
[0025] The method according to the invention has the features of
the annexed independent claim 1.
[0026] Advantageous embodiments are described in the dependent
claims.
[0027] The method therefore constitutes an alternative to the
traditional system of combustion in incinerators of the MSW and of
the fuels derived therefrom and to their dumping.
[0028] The method also constitutes an alternative to those already
implemented industrially or proposed by the same Applicant as
demonstrated in the prior art.
[0029] Referring to FIG. 1, the process can be schematised as
follows: [0030] a) Biostabilisation by the method described in EP
0706839 and EP 1386675 with the object of transforming MSW into a
dry and homogeneous material with piece size of around 20-30 cm and
which can be treated easily (RDF). [0031] b) Compacting of RDF into
bales or BIOCUBI.RTM. with size of around 1.times.1.times.2 in and
storage of the BIOCUBI.RTM. in the bioreactors as described in EP
1520634 and WO2005102547. [0032] c) Activation of the bioreactors
by wetting with water to produce biogas: the sizes of the
bioreactors are such as to form large reservoirs of biogas and the
times for the completion of the anaerobic process are reduced so as
to make available in a shorter time, compared to a conventional
landfill, (5-6 years) the non-biodegradable residue formed by inert
and plastic. The biogas produced is purified of the possible
residual traces of chlorinated products by means of known
techniques, e.g. passage over active carbon beds. [0033] d)
Combustion at the start of RDF and subsequently of the residue
already digested in the bioreactors, and therefore
non-biodegradable, in a waste combustor equipped with a system of
purification of exhaust gasses and production of superheated steam
at approximately 400.degree. C. and pressure around 70 bars. [0034]
e) Combustion of the purified biogas in a conventional boiler
equipped with re-superheaters for raising the temperature of the
steam produced by the waste combustor by approximately 100.degree.
C. [0035] f) Use of the steam produced in this way in a turbine
coupled with an alternator for the production of electrical
energy.
[0036] A further possible integration presented in FIG. 1 is
represented by the use of the contaminated air released by the
process of bio-drying for the combustion of the waste.
[0037] In this way it is possible to eliminate, wholly or in part,
the treatment of the air released by bio-drying.
[0038] Bio-drying is described in detail in the aforementioned
patents and serves to dry and stabilise the waste and produce
substrates that can be activated and are particularly reactive for
the anaerobic digestion in the bioreactors.
[0039] To sum up, the waste and in particular the MSW is fed in a
closed space where it is ground roughly and arranged in layers on a
floor with holes which is divided into sectors through which the
air is passed: aerobic digestion of the putrescible part develops
heat which evaporates the water which is removed with the air
flow.
[0040] Starting with 100 kg of MSW having a humidity content of
around 36% and a lower heating value (LHV) of 2200 kcal/kg, 75 kg
of RDF are obtained with a humidity content of around 19% and an
LHV of around 2900 kcal/kg.
[0041] The product obtained in this way is odourless and stable,
can be compressed into bales or BIOCUBI.RTM. with density of around
700 kg/m.sup.3 and placed in the bioreactor.
[0042] The BIOCUBI.RTM. can be produced on site or easily
transported from production systems distributed in the
territory.
[0043] The bioreactor is also divided into sectors as described in
WO2005102547 so as to activate it by injecting water into each
sector in sequence over the years and have a continuous production
of biogas and at capacity a tank and continuous availability of
exhausted material at the end of the life of each sector.
[0044] In time it may be possible to reduce the use of water,
replacing it with percolates or other liquid effluents containing
digestible substances and therefore able to form an additional
source of biogas.
[0045] The bioreactors are completely covered by a polymeric
membrane, which ensures the containment of the biogas produced and
are equipped with internal manifolds for its collection.
[0046] They therefore represent large tanks suitable for
guaranteeing availability of the gaseous fuel for the process.
[0047] When a sector ends production, the biodegradable portion
being exhausted and the part composed of soil, plastic and part of
the wood remaining, air is aspirated or blown so as to eliminate
part of the residual water and obtain a humidity content of between
20 and 25%.
[0048] Optionally, in order to accelerate evaporation of the water
and/or obtain low residual humidity of the waste, hot air or
mixtures of air/gasses from the combustion could be used (not shown
in the drawings).
[0049] Again on the basis of 100 kg of MSW initially, the product
of the bioreactors is typically 59-63 kg of exhausted material
having an LHV of around 2700-2600 kcal/kg.
[0050] 15-20 kg of biogas are also produced with a content of
methane of around 45-55% in volume, according to the nature of the
initial material, and having an LHV of around 2900 kcal/kg.
[0051] At this point the significant reduction in the solids fed to
the combustor and the improvement in the energy content of the
fuels to be burnt compared to the initial MSW should be noted.
[0052] The combustor of the solid waste has a reduced load and with
improved efficiency and the purified biogas is used partially or
totally in an additional boiler for re-superheating the superheated
steam, allowing the limit of 400.degree. C. of conventional
combustors to be exceeded.
[0053] Referring to the diagram of FIG. 2, the combustor is for
example composed of a grate furnace provided with a boiler for the
production of superheated steam at 400.degree. C. and 70 bar,
equipped with the combustion gasses purification line formed by a
series of cyclones for abating the substantial part of the solids
conveyed, a cooling tower for controlling the temperature, a
reactor fed with lime and active carbons for the neutralisation of
the residual acidity and the adsorption of the micropollutants and
a bag filter for retaining the fine dust before emission at the
stack.
[0054] The superheated steam generated in the boiler, and possibly
a share of control water, is sent to the superheater fed with
biogas where the temperature of the steam is raised by around
100.degree. C. according to the biogas available.
[0055] This steam, expanded in the turbine, allows a yield of the
thermal cycle of FIG. 2 of around 32% to be obtained and therefore
similar to that which can be achieved with the waste combustor
coupled with a thermoelectric plant.
[0056] The results obtained with the invention claimed here are
given in the following examples of application, based on the
experience of industrial bio-drying systems, on experiments of a
system for the production of biogas and on available waste
combustors.
EXAMPLE
[0057] The intent is to build a large waste combustor having a
supplied thermal power of 110 MWt such as that in FIG. 2, using the
innovative cycle, which is the object of the present invention,
shown schematically in FIG. 1.
[0058] The combustor is fed with 34 t/h of solid waste obtained
from the bioreactor starting from 43 t/h of RDF obtained in turn
through bio-drying from 58 t/h of MSW.
[0059] The boiler of the combustor produces, dispersed heat
accounted, 122 t/h of steam superheated at 400.degree. C. and 70
bar which is sent to the re-superheater fed with 6.8 t/h of biogas
produced in the bioreactor.
[0060] 128 t/h of superheated steam are produced at 492.degree. C.
of which 6 t/h of steam from temperature control added water.
[0061] This steam, expanded in the turbine, generates, including
the yields of the machines, 35.5 Mwe with a yield of the
thermoelectric cycle of over 32%.
[0062] The process plan proposed therefore represents a valid
alternative to the integration of the waste combustor with a
thermoelectric plant if this plant is not available on site.
[0063] The large reduction in the solid waste to be burnt compared
to the combustion of RDF and above all of MSW should be remarked,
thanks to the production of the biogas that, in the process, which
is the object of the present invention, serves to raise the heat
level of the steam and therefore the yields of the entire
cycle.
* * * * *