Cofiring of biomass with municipal solid waste and sludge in Brescia waste incineration plant

ALTENER International AFB – net cofiring

WORKSHOP EUROPEAN EXPERIENCE IN BIOMASS COFIRING

Grenoble 13 – 14 September 2000

Cofiring of biomass with municipal solid waste and sludge in Brescia waste to energy plant (grate, 45 Mw el – 102 MW th)

Antonio Bonomo ASM BRESCIA Spa

2

INDEX

Summary 0.

Introduction

1.

Sustainable development

2.

The waste emergency

3.

The Brescia Integrated System for Waste Management

4.

Separate waste collection

5.

The background of the energy from waste plant

6.

Milestones of the WTE project

7.

Energy recovered

8.

Clean residues

9.

Plant design aspects

9.1

Environment protection

9.2

Energy recovery net efficiency

9.3

Operation reliability and safety

10.

Investment and operation cost

1

Summary On 21th March, 1998, after two and a half years from the beginning of construction, the Waste to Energy plant of Brescia (2 x 88,3 MWth – 2 x 23 t/h waste) had its first waste combustion.

Now the plant is in the industrial operation phase.

By 31st august 2000, 860.000 t of waste and biomass were utilised, with a net production of 536 GWh of electricity and 512 GWh of heat for the district heating network.

The plant provides to the city of Brescia (200.000 inhabitants) electric energy (200 GWh/a) and heat (350 GWh/a), i.e. a quarter of its energy needs.

The WTE plant is an essential part of the "Brescia Integrated Waste Management System”, approved by the City Council and implemented starting from 1992, with a great involvement of all citizens.

The aim of such Integrated System is the maximum recovery of waste: -

materials (from separate collection of usefully recyclable waste)

-

energy (from the remaining waste) .

Great attention has been given to protection of the environment and to net efficiency of energy production with the consequence that a parity of electricity and heat generated, the emissions are lower than those produced by coal, oil and gas fueled power plants.

Biomass is also cofired with waste with a percentage that can vary from 0 to 80%.

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0. Introduction

In a "sustainable development" concept and within an integrated management system, waste should be regarded as a resource for materials and energy recovery and not simply as a product for disposal.

After source separation of recyclable materials, a considerable amount of waste remains and the heat value of this residue is significant.

Further, it is a renewable energy source, as it is mainly made by vegetablecellulosic substances; the non renewable components which are present, for instance plastic, would otherwise be disposed of by landfill, which permits only very little energy recovery.

Energy production from waste shall occur with great care to energy efficiency, as done in biomass fueled plants.

The efficiency of energy production is an important environmental protection factor, as it allows both the saving of non-renewable energy resources and the avoidance of emissions from power plants fired with traditional fossil fuels.

If waste to energy plants are energy efficient, emissions may be lower (per unit of net energy generated), than from conventional fossil fuel fired plants.

In the future, if plants are highly efficient, they could also be used for biomass fuel, when the waste reduction priority strategy has been successful.

It must be stressed that the net global energy efficiency must be taken into account when comparing different waste management and energy recovery processes. It is important to consider the whole process, including

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collection, transportation, pretreatments, treatments, residue disposal, etc.

As indicated in latest EU directives, the choice between material recycling and energy recovery should be made case by case, within a integrated waste management system and by using best-practice methods for the protection of environment.

It is also important to develop cost-effective solutions, as this can encourage the adoption of best-practice methods.

The above concepts were the guidelines for the developing of the Brescia Integrated Waste Management System and, within it, of the WTE plant, which is now in the trial operation phase.

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1.

Sustainable development

Though scientific and technological progress has brought undeniable advantages to mankind, the effect on the environment of an excessive consumption of raw materials has often been underestimated.

The European Union has become aware of this, and has decided to promote forms of sustainable growth: this is an option that allows for development, without compromising the availability of resources and the quality of the environment for future generations.

The idea behind this choice is the use of renewable resources, obtainable within a type of economy that respects the cycles of Nature.

Waste form an important part of this picture: advanced societies are producing more and more of it, while disposal becomes more and more difficult.

This emergency calls out for innovative global strategies, which need suitable organisation.

The city of Brescia (200.000 inhabitants) is facing up to this problem through its Utility (ASM BRESCIA SpA), to which the Town Council has delegated the management of the waste sector: control, recovery, recycling, upgrading and disposal.

2.

The waste emergency

Over the last twenty years, the amount of waste disposed of in landfills in the Province of Brescia (1.050.000 inhabitants) has increased exponentially: from 60,000 tons in 1973 it grew over 450.000 tons in 1997.

This strong increase depends not only on the amount of waste produced, but also on the progressive elimination of unauthorised dumps.

5

It was in fact these figures that convinced ASM Brescia, with its experience in the waste field, to draw up a plan for a global solution to this problem.

For over twenty years ASM Brescia has been involved in the separate collection of waste, which it has encouraged through information campaigns directed at the town citizen, who have become protagonists in the process of separation and recovery.

The conditions become ripe for a further step: the Integrated System for the management of solid urban waste, approved by the Brescia Town Council on 28th July, 1992.

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3.

The Brescia Integrated System for Waste Management

The reduction of the waste we produce and, where this is not possible, its separation, recycling and conversion into energy followed by the correct disposal of what is left: these are the key points of the Brescia Integrated System, designed to bring the ideas of the European Union into reality, ideas that are expressed also in the Italian and the Lombardia Region legislation.

In the field of waste, E.U. requires: .

limitation of waste production

.

recovery of materials and energy

.

recycling of these materials in production processes

.

use of treatment and disposal systems that are

compatible with

human health and the protection of the environment.

The ASM project was discussed and verified by a "Technical-scientific Committee", nominated by the town authorities in the summer of 1991, whose members were experts in technical, environmental and social fields.

The contribution of different disciplines led to a clear line for waste management and to an overall strategy that follows a so called "double rail": -

on one hand, reduction of the amount of waste produced, its separation and recycling, through the conscious collaboration of both inhabitants and businesses

-

on the other hand, the development of efficient technologies for the recovery of energy from waste that cannot be usefully recycled, and the transformation of organic waste into fertiliser.

Landfills will be used only for materials that are substantially inert, including residues from the energy from waste (EFW) plant.

7

To help in this ambitious project, in 1992 ASM set up a specific "Waste observatory", with the job of analysing and co-ordinating the various initiatives for increasing the recovery of waste, classifying it by origin, composition and quantity.

This observatory also keeps an eye on the various separate waste collection processes, and evaluates each initiative for its environmental, energy and economic effects.

4.

Separate waste collection

In Brescia the separate waste collection for material recycling is continuously increasing.

This is partly a result of the information ASM gives its citizens and of the support to similar campaigns promoted by various other groups and associations.

A few figures serve to illustrate this: in 1997, 33,000 tons of waste were collected separately, equal to 29% of the total; in 1991, before the starting of the Integrated System, the figure was 5,750 tons, equal to 6.3% (see fig.

1).

The goal of 36% of recycled waste, fixed in the project approved in 1992, is now not so far. Nevertheless the work of information and campaigns continues without a pause.

8

Figura n. 1 – Waste separate collection in Brescia

9

5.

The background of the energy from waste plant

In the late sixties and early seventies, ASM introduced a new way of heating the town buildings: the district heating; now 120.000 inhabitants are supplied by D.H. through 400 km of double hot water pipes.

Therefore there was in Brescia an optimal condition for extensive use of energy recovered from waste: both electricity and heat, with a possible total efficiency of over 80%.

An important contribution to the ASM project was given by the Technical – Scientifical Committee set up by the Town Council in 1991, composed of: national experts in the energy, environment and medical field, researchers of University of Brescia, representatives from local administration (Town, Province, Region and Health Authorities) and representatives of the ecology movement.

The Committee operated at the unanimity and its recommendations, including the siting of the WTE plant, were approved by the City Council on 28th July 1992.

In August 1993, finally, the Lombardia Region granted the final permit for the construction.

In the mean time there have been many information campaigns and occasions for debate on this subject.

To this regard, it is to be outlined that involvement and consent of public are essential factors for the success of the WTE project.

As well as many public meetings, newspaper articles and television programmes, three international scientific conferences have been held in Brescia, in 1991 “Waste to energy. An integrated solution for Brescia”), 1993 (“Towards new environmental solidarities”) and 1998 (“Waste to energy. A step towards the renewable energy”).

These events allowed a thorough airing of the subject and comparison with

10

advanced foreign experiences in the field, confirming that the Integrated System is the most suitable solution for the Brescia situation.

11

6.

Milestones of the WTE project

31.5.1991

Presentation to the Brescia public of the ASM plan for an energy from waste plant at international conference "Energy from Waste - an Integrated Solution for Brescia".

11.7.1991

Resolution No. 3105 of the Brescia Town Council Executive: nomination of the Committee of experts, to examine and evaluate all aspects of the plan to build a treatment plant for solid urban waste, with recovery of heat and electricity, and to chose its location

2.4.1992

Deliberation of the ASM Board of Administrators (based on the recommendations of the technical-scientific): Guidelines for the management of solid urban and similar waste (Integrated Brescia System) Energy from waste plant

April - July 1992

Numerous meetings and debates to illustrate and discuss the project with various bodies (often with the presence of the technical-scientific Committee of experts): Town Council Commissions Town Council _ Town Districts (particularly in the 5th, 6th and 7th Districts).

28.7.1992

Deliberation of the Town Council: No. 114 - Guidelines for the management of solid urban waste No. 115 - Plans and action to increase separate waste collection and recycling No. 116 - Energy from waste plant

September 1992

Presentation of the energy from waste plant project to the Region for approval.

International Conference "Towards a new environmental solidarity" for the presentation of the Integrated System to the Brescia public, and its comparison with other advanced experiences in the management and recovery of waste.

20 – 21.5.1993

1.7.1993

Regional Law No. 21 on the regional plan for disposal of waste, wholly accepting the guidelines of the Integrated Brescia System and the criteria behind the ASM EFW.

2.8.1993

Regional Resolution No. 40001: final approval of EFW plant construction.

22.9.1993

Publication of tender conditions in the European Community Official Gazzette.

March 1994

Conclusion of the selection of firms admitted to tender, as having the necessary experience.

3.4.1995

Signature of contract for the supply of the EFW plant.

October 1995

Start of construction work.

21.3 1998

First waste combustion

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7.

Energy recovered

The plant will become a valuable source of energy for the town of Brescia.

Thanks to the presence of the district heating system, it will be possible to recover not only electricity (as in many other similar plants) but also a remarkable amount of heat.

With the plant running at its full initial capacity, it gives 200 million kilowatthours of electricity and 350 million kilowatt-hours of heat per year, with an annual saving of 80,000 tons equivalent of oil.

This corresponds to about a quarter of the energy supplied to Brescia by ASM in 1997.

If needed, a third combustion unit, which at the moment exists only at project level, could be installed in the future. In this case the electricity recovery will be 300 million kilowatt-hours a year, and the heat recovery 450 million, while the annual energy saving will be 120,000 tons equivalent of oil.

8.

Clean residues

The WTE plant is in effect a "waste cleaner", as the high combustion temperature eliminates the organic components and leaves clean residues; the metallic substances that combustion cannot destroy are concentrated in a small quantity of residues, in powder form.

During the design stage, particular attention was given to the problem of the treatment of combustion residues: each line has its own hermetically sealed system for the removal of residues and the removal of dust from the boiler and filters.

Combustion slags (equal to about 20% of mass of the waste treated), are

13

used in authorised landfills, as substitution of gravel for daily covering of waste and for internal roads; dust from the gas cleaning is submitted to a specific inertization process and then finally disposed of.

A slag selection and treatment process is under study, aiming to recycling the slag and reusing them as a substitute for gravel in a road construction, thus saving quarry natural resources.

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9.

Plant design aspects

Figures 2 to 5 summarise the main technical data of the plant.

Figures 6 to 9 show respectively the plant model view, longitudinal section, flue gas cleaning system, thermal cycle.

The essential goals of the project have been: 1.

high environmental protection level

2.

high net efficiency of the energy recovery

3.

high reliability, safety and availability

9.1

Environment protection

The following solutions have been adopted: .

closed building, kept at negative pressures (including the waste trucks unloading building)

.

advanced combustion system for minimisation unburned and NOx -

fully automatic regulating system for the waste feeding, grate movement and combustion, by means of an "expert" system guided by two infrared camera installed on the top of the combustion chamber

-

automatic and independent dosing of the combustion air for each one of the 30 compartments under the grate

.

recirculation of flue gas into the combustion chamber

fully dry gas cleaning system using calcium hydrate and active carbons to cut down drastically the micro pollutants (both heavy metals and chlorinated components).

.

automatic optimisation of the flue gas temperature before the gas cleaning by means of an accurate control loop (1°C precision)

.

high performance fabric filter , consisting of 6 independent sections, individually interceptable, with the possibility

of inspecting

and

15

substituting the filtering elements of one section while keeping in operation the other 5 . .

reagent silos and dosing equipment fully redundant.

.

continuous monitoring system of the emissions by using advanced type redundant analysers (separate measurements for the regulating system and the supervision)

.

very low water consumption with no liquid effluents

.

use of components

with low acustic emissions (75 dBA) and

appropriate noise insulation.

Fig. 10 and 11 show design emission limits and the first operational results.

Thanks to low emission limits and high energy efficiency, 200,000 tons of CO2 emissions are avoided, compared to the alternative of landfilling the waste and of producing the same amount of energy with fossil fuels (in the Brescia case, oil for electricity generation and natural gas for buildings heating); at the same time, dust and SO2 emissions are reduced by over 90%, and NOx emissions by 50%.

9.2

Energy recovery net efficiency

The efficiency is maximised by means of: .

low combustion air excess (4 to 7% O2)

.

high energy recovery from the cooling of the flue gases : from approx. 1100 to 130°C

.

combustion air preheating by turbine extraction steam

.

low auxiliary power consumption (each consumed kWh means one kWh not recovered) -

semplicity of the process wherever possible and coherent with

the

aforesaid

guidance

principles;

e.g.

unnecessary treatments and transports of the waste.

avoid

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-

equipment with a high efficiency in the actual working conditions, e.g. variable frequency motor drives

.

high efficiency of the thermodynamic cycle : -

high parameters of steam pressure and temperature: 60 bar and 450°C (guaranteeing plant reliability at the same time)

-

turbine and thermal cycle of the regenerative type, designed "ad hoc"

.

electric power and heat cogeneration (for the district heating network)

Th resulting net efficiency, referred to the lower heating value of waste, is from 23 to 26% (depending on degree of cogeneration) for electricity and 61 to 54% of heat; the total net efficiency is 80÷83%, depending on LHV of waste.

9.3

Operations reliability and safety

.

implementation of well proven technologies and use of high quality and certified components

.

redundant components for the most critical systems

.

high level of monitoring and automation systems of the plant (15000 parameters measured and transmitted up to the main control room)

.

distributed control system (DCS), (the lower hierarchic levels – n. 3 in total - can operate even in case of failure of the upper levels)

.

double process measurement devices for the redundancy of the regulating systems ***

Even if the plant is still in the trial operation and acceptance test phase, the first operating experience shows a good correspondence with the design goals.

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10.

Investment and operation costs

In fig. 12 and 13 the main data regarding investment and operation costs are summarized.

1

Fig. 2

BRESCIA WTE PLANT

GENERAL DATA

Turn key supplier:

Consortium ANSALDO-MARTIN –ABB

Materials treated:

solid urban and similar waste - dried sludge from sewage treatment plants biomass

Nominal capacity:

46 t/h (2x23 t/h) (at lower heating value of 3300 kcal/kg 13816 kJ/kg)

Combustion lines:

2 (with allowance for a future third line)

Waste unloading:

in closed, negative pressure hall

Waste storage capacity:

30,000 m3

2

Fig. 3 BRESCIA WTE PLANT

COMBUSTION LINES (data referred to each line)

Supplier of stoker grate:

MARTIN GmbH (Germany)

Supplier of steam generator:

ANSALDO Spa (Genoa, Italy)

Thermal capacity:

88.3 MWt

Allowable lower heating value of waste:

from 6280 to 13816 kJ/kg (1500 - 3300 kcal/kg)

Combustion grate: -area:

103 m2

-No. of steps:

15

-combustion regulation:

feeding and movement of waste and regulation of primary and secondary air: through a fully automatic "expert system", guided by infra-red cameras

-combustion air control:

automatic and independent for each of the 30 grate sectors

Combustion temperature:

>1100 °C

Post-combustion temperature:

>950 °C for over 2 secs

Superheated steam pressure:

60 bar

Superheated steam temperature: 450° C

3

Fig. 4

BRESCIA WTE PLANT

GAS CLEANING SYSTEM (data referred to each line)

Supplier:

ABB Sae Sadelmi (Sweden Italy)

Gas conditioning inlet:

cooling to 135 °C with full heat recovery

Reagents injection:

dry

De-acidifying agent:

powdered lime Ca(OH)2

Micro-pollution removal agent:

active carbon

Final filtering:

Fabric filters

Filtering area:

5000 m2

Filtering speed:

<1m/min

Filter material:

Ryton-rastex

Dust inertization:

with cement + additives

Nox removal:

SNCR type, with NH3 injection (supplier: Martin GmbH)

4

Fig. 5 BRESCIA WTE PLANT

ENERGY RECOVERY SECTION

Supplier:

ANSALDO Spa (Genoa, Italy)

Type:

turbine

generator

unit

(in

common to the combustion lines) Steam turbine:

condensation and extractions

Electricity self consumption:

12%

Generator voltage:

15 kV

Steam condenser:

air, dry

Condensation pressure:

0.1 bar at T atm. = 20 °C

District heating section:

P= 16 bar Tmax = 130 °C

Net power produced (2 lines running, LHV 3300 kcal/kg): - electricity:

45 MW

- district heating:

102 MWth

Net annual energy recovery (LHV = 2500 kcal/kg): - electricity:

200 GWhe/a

- district heating:

350 GWht/a

Saving of fossil fuel:

80,000 Teq/year (equivalent tonnes of oil per year)

12

Fig.n.10 Emissions limits of Brescia WTE plant and comparison with limits imposed by laws (mg/Nm3) Components

European Union (1989)

Regional Authorisation (1993)

Italy

ASM project

(future plants)

ASM first Operation results

(1998)

7/1998 Dust

30

10

10

5

<1

SO2

300

150

100

100

<30

Nox

-

200

200

<100

<100

HCl

50

30

20

20

10

HF

2

1

1

1

<0,2

CO

100

100

50

50

10

Pb+Cr+Cu+Mn

5

}2

} 0,5

} 0,5

} 0,015

Ni+As

1

Cd

} 0,2

0.1

0.05

0.05

<0,001

0.1

0,05

0.05

<0,001

0.1

0,1

0.1

<0,001

Hg TCCD(Teq-ng/Nm3)

-