The Mondi Merebank MultiFuel Boiler

Presented by Mark Miller

Date February 2010

The MultiFuel Boiler

South African Division

South Africa Division

Forests Richards Bay Merebank

• The leading brand in South Africa

• Key market South Africa

• Long standing reputation for all-round performance

• The paper for everyday use with high whiteness

• Ideally suited for use in inkjet and laser printers, copiers and fax machines

• Pioneer in FSC (Forest Stewardship Council) certification

Merebank: Core products -Domestic

Merebank: Core products -Export

• No. 1

• Copyrex

• Niveus Top

• Dolphin

• Southern Star

All available in 80gsm, A4 & A3

The Paper Making ProcessWood to chipsDebarkingSawingChippingScreening

Chips to PulpCookingWashingBleachingRefining

Pulp to paperFormingPressingDryingWinding

FinishingCuttingSizingWrappingPackaging

The Paper Making Process – Energy Intensive

To make paper is energy intensive.

The Merebank Mill typically consumes 125 MW of electricity.

This makes Mondi the biggest consumer in the Ethekwini Municipality

The second largest consumer in the boundaries of the Municipality is Toyota which consumes only a third of that of the Merebank Mill

This energy intensiveness demands an effective approach to Energy Efficiencies and Cost Effectiveness

The Paper Making Process

Significant quantities of low pressure steam are re quired

Mainly used to dry the wet paper sheet through the transfer of latent heat from the saturated steam through the drying cylinders

Up to 210 tons/hour of 5 bar saturated steam required with all machines operational

The steam were produced in the past with 2 x 85 tph coal fired stoker boilers

Make-up steam were generated with a 23 tph and 55 tph gas boiler

Two 25 tph oil boilers were used as standby boilers

It was possible to generate up to 9 MW of power using existing back pressure turbines

Waste Products

Waste Products produced (pre project)

Waste water from the water treatment plant. Recovered in belt pressesSignificant CV value due to fibre

Bark and saw dust from the debarking and chipping process.

Coarse ash from the coal boilersCarbon remnants for possible reburning

Waste as Fuel

An analysis of the typical waste products potentially available as fuel

Coal Bark Sawdust Sludge Coarse

Ash

Fine Ash

Cal. Value

(MJ/kg)

26.12 7.13 7.4 3.12 8.18 11.81

Mass Flow

(tons/day)

156 95 35 231 86 64

Input

Energy (%)

57 9 4 10 10 10

Steam flow

(tons/h)

51 8 3 9 9 9

The Multi-fuel Boiler - Strategic Significance

Mondi decided in the early 2000’s to install a new multi-fuel boiler. It made strategic sense:

Reduce landfill costs

Reduce environmental impacts

Secure sufficient and reliable steam resources for present and foreseeable future needs

Allow Mondi the opportunity to generate more electricity to counter rising electricity costs

Allow the mothballing of the aging oil fired boilers, thereby reducing the site SO2

emission levels

Transfer the gas boilers to standby, significantly reducing the cost of steam production

The Multi-fuel Boiler

Mondi decided to purchase a 90 tph bubbling bed fluidised boiler (BFB). Advantages over conventional boilers:

Compact size

Fuel Flexibility

High Combustion efficiency

Reduced emissions of noxious pollutants such as SOx

Relatively wide operating ranges

Low Combustion temperatures(800 – 900 oC)

Limestone is injected directly into the furnace to control SOx emissions

Fuels: natural gas (as a start-up fuel), coal, bark, sawdust, fine ash, coarse ash and sludge.

Coal is required as the base fuel

New Turbine

A 21.7 MW (27 MVA) back-pressure turbine-generator set was purchased with the boiler to generate electricity.

The Multi-fuel Boiler

The main features of the BFB are:

A low and evenly distributed bed temperature, high turbulence, and long residence time, all optimise the combustion process

In bed tubes to increase heat transfer

Grits re-firing to increase boiler efficiency

Lime stone injection directly into the furnace

Bag filters to reduce particle emissions

Metso DCS System

The Multi-fuel Boiler

The Multi-fuel Boiler – Material Handling

The challenges of material handling systems:

Site space constraints

Limited availability of certain fuels, inducing the need for buffer bins and silos

Special mixing requirements

Accurate control of fuel feed to ensure proper combustion

Removal, screening and recirculation of sand from the bed

Complicated over and under bed gas firing system

Fluidising ducting, piping and nozzles

Fuel re-feed systems

The Multi-fuel Boiler – Material Handling

The Multi-fuel Boiler - Integration

The MFB was designed to produce 90 tons/hour @ 65 Bar, with a superheated steam temperature of 475 oC

The MFB was designed to be the base load boiler, with the two coal boilers making up the difference

The new turbine was sized to produce 21.7 MW @ 65 Bar with an input steam requirement of 154 tons

The remaining steam obtained from the two coal boilers

LP steam leaves the turbine outlet 5 Bar

The LP steam (with backpressure control from the turbine) is sent to the Mill to satisfy the Mill steam requirements (mainly paper drying)

Original Steam System

C urren t S team S ys tem

O il30 t/h

C oa l85 t/h

O il30 t/h

C oa l85 t/h

G as30 t/h

1

3

5

6

4

4 .5 MW

4.5 MW

5 B ar, 163 oC

Sta

nd-b

yP

rodu

ctio

n

T o M ill62 Ba r, 485 oC

15 Bar, 220 oC

18 Bar, 212 oC

G as50 t/h

15 Bar, 220 oC

P R D S

P R D S

P R D S

P R D S8

Sta

nd-b

y

75T P H

75T P H

23T P H

39T P HS/W ater

5T PH

205T PH

T o M ill

30T PHT o M ill

N o te : If the M FB w ere no t insta lled , bo ile r 8 w ou ld be sw itched from standby to run fu ll tim e to cover the s team requ irem ents

N ote : P R D S = P ressure R educ ing S ta tion

New Steam System with MFB and Turbine

C oal85 t/h

M ulti-fue l90 t/h

G as55 t/h

8

5

6

7

4

4.5 MW

4.5 MW

20.8MW

Boiler N o.

Sta

nd-b

y G as30 t/h

Pro

duct

ion

5 Bar, 163 oCTo M ill

Steam S ystemW ith M u lti-Fuel Bo iler

NE W

To M ill5 Bar, 163oC

18 Bar, 212 oC

79tph

82 tph

C oal85 t/h

79tph

235tph

5tph

N ote . Spray water contribution w ill be sm all and has been ignored for calculation purposes

PRD S

PR D S

PR D S

PRD S

N ote : PR D S = Pressure Reducing S ta tion

Understanding fluidised bed combustion

Fluidised bed combustion differs from conventional pulverised coal combustion.

Continuous stream of air to create turbulence in a mixed bed of fuel, inert material and coarse fuel ash particles.

Combustion occurs at lower temperatures typically between 800°C and 900°C.

Fluidised bed combustion (FBC) technology is particularly suitable for coals that are difficult to mill and fire in pulverised coal combustion boilers.

FBC technology is commercially available for modules up to 300 MWe, with a number of projects being planned or presently implemented in the 250–350 MWe size range.

FBC represents about 2 per cent of the total coal-fired capacity worldwide but it is expected to be further adopted for a other applications.

Understanding fluidised bed combustion

Fuel is fed onto a packed bed of inert particles (sand).

An upward air flow fluidizes the bed via a distributor to provide uniform flow of air across the whole base area of the fluidized bed

If the upward air flow is turned off the particles can become de-fluidized or slumped

Fuel is burned in the bed and at times in the freeboard above the bed. (Combustion of around 800–900°C - considerably lower than in pulver ised coal combustion)

The freeboard can be designed with a much larger diameter than the bed. The reduced gas velocity in the section ensures that coarse solid particles entrained in the gas flow fall back to the bed by gravity. Fine particles (which encourage abrasion) are carried forward with the flue gas

Secondary air, is introduced into the freeboard region to ensure complete combustion of the fuel.

Fluidized bed combustion

After exiting the combustor, the flue gases pass into a convective section where heat is

further recovered and the gases are cooled to below 200°C.

Then through a particulate control unit that can be a cyclone, a bag filter or an electrostatic precipitator. The cleaned gases are finally discharged into the atmosphere through a stack.

Combustion leaves behind the mineral matter in the coal and the spent sorbent (if added when sulphur removal is required) in the bed.

Coarse particles can accumulate in the bed. Excessive material is removed by an off-take from the bottom of the bed or via an overflow weir. This ensures the bed is maintained at the

designed depth

Good Bed Management is required

Fluidized bed combustion

When the gas velocity exceeds the minimum fluidising velocity, the excess gas passes

through the bed as bubbles. Practically gas velocities are several times higher than the

minimum fluidizing velocity.

Bubbles passing through the bed typically occupy 20–50% of the bed volume. The passage

of the bubbles, in upwards and sideways coalescing movements, gives intensive agitation

and mixing of the bed particles.

Fluidising velocity is perhaps the most important parameter of fluidisation. Its choice affects

most of the other process parameters. It typically ranges from 1 to 3 m/s for bubbling fluidised beds

The bubbling bed

Air Systems

In Bed Tubes

In Bed Tubes

Nozzles

Bark, Sludge & Sawdust Delivery

Bark, Sawdust & Sludge to Boiler

The Multi-fuel Boiler – Benefits Review

The MFB allowed Mondi to retire the two oil boilers – reduced environmental impact

Significant reduction of waste products = cleaner environment

The two gas boilers now standby

Steam supply is now reliable and secure – less unplanned shuts

The new turbine improved volt dip immunity and reduced electrical import

The improved Boiler standby capacity allows improved maintenance on the boilers and hence reliability of the steam system

Lessons Learned

Research and design is a worthwhile investment

Involve the local community

Use well proven technology

Good planning is essential

Have a good contract in place

Automation is key in leading technologies

Good troubleshooting and information gathering tools

FORWARD - LOOKING STATEMENTS

It should be noted that certain statements herein which are not historical facts, including, without limitation those regarding expectations of market growth and developments; expectations of growth and profitability; and statements preceded by “believes”, “expects”, “anticipates”, “foresees”, “may” or similar expressions, are forward-looking statements. Since these statements are based on current knowledge, plans, estimates and projections, they involve risks and uncertainties which may cause actual results to materially differ from those expressed in such forward-looking statements. Various factors could cause actual future results, performance or events to differ materially from those described in these statements. Such factors include in particular but without any limitation: (1) operating factors such as continued success of manufacturing activities and the achievement of efficiencies therein, continued success of product development plans and targets, changes in the degree of protection created by Group’s patents and other intellectual property rights, the availability of capital on acceptable terms; (2) industry conditions, such as strength of product demand, intensity of competition, prevailing and future global market prices for the Group’s products and raw materials and the pricing pressures thereto, financial condition of the customers, suppliers and the competitors of the Group, potential introduction of competing products and technologies by competitors; and (3) general economic conditions, such as rates of economic growth in the Group’s principal geographical markets or fluctuations of exchange rates and interest rates.

Mondi does not

a) assume any warranty or liability as to accuracy or completeness of the information provided hereinb) undertake to review or confirm analysts’ expectations or estimates or to update any forward-looking statements to reflect events that occur or circumstances that arise after the date of making any forward-looking statements.