balance steam supply with demand_ then save energy and reduce carbon footprint

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Balance steam supply with demand: then saveenergy and reduce carbon footprint

Brazils Cenibra pulp mill sees a 90% reduction in vented steam after

Metsos Steam Manager APC is installed. Fuel costs are down and the carbon

footprint of the power boilers has been slashed by the equivalent of 2, 200

tons per month of CO2 emissions.

Click here and ask for more information.

Keeping a balance between steam supply anddemand is a challenging task in a multi-line pulpmill complex, since there are always manysources of supply and multiple users of steamenergy. But pulp mill processes are dynamic andoften in transition. So if this delicate equilibrium isdisturbed on the supply side or at the demandside, it is quite common for the steam network toget out-of-balance, which can result in steamsupply variations. Some key processes may lack

steam or steam may be vented, both of whichwaste energy and money. Typically, when processsteam demand is not met by primary sources,auxiliary boilers are used to make up thedifference, often using more expensive non-biofuels like oil or gas, And, when excess steam isvented a lot of valuable fuel and money is wasted,and this adds to the carbon footprint of the mill.

To keep that ideal balance point and with an eyeon saving boiler fuel and reducing carbonemissions Celulose Nipo-Brasileira S.A. (Cenibra)commissioned a Metso Steam Manageroptimization control for the steam supply anddistribution system of its ECF bleached eucalyptus fiber pulp mill in Minas Gerais, Belo

Oriente, Brazil. The mill is owned by Japan Brazil Paper and Pulp ResourcesDevelopment Co., Ltd. The total production from two fiber lines is 1 160 000 tonnesper year, 92% of which is exported. Cenibra, one the largest pulp producers in Brazil,is also a pioneer since it was established in 1977.

In this article you willlearn:

The pulp mill achieved a90% reduction in ventedsteam after Metsos SteamManager APC is installed.

Fuel costs are down and

the carbon footprint of the

power boilers has been

slashed by the equivalent

of 2, 200 tons per month

of CO2 emissions.
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The commissioning of the Steam Manager advanced process control (APC) system inMay 2009 has paid off handsomely as vented steam has been reduced by anastounding 90% and the steam supply has been stabilized. Steam consumption islower and Steam Manager meets our expectations, reducing costs and this is reflectedin oil consumption, reports Rbinson Flix, Mill Manager.


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Steam consumption is lower and Steam Managermeets our expectations, reducing costs and this isreflected in oil consumption, reports Rbinson Flix,Mill Manager.

Improving stability, lowering costs

The decision to commission Steam Manager was part of a larger, more comprehensiveplan by the mill to optimize many of its mill processes to improve process stability,produce uniform quality and lower costs. Altogether, five Metso APC systems havebeen commissioned in the mill.

The Steam Manager project was a collaborative effort between partners- Metso andCenibra - who had been working together for many years. When asked why theychose Metso, Ronaldo Ribeiro,Automation Specialist says, This was a long termprocess. Metso was selected because we have worked seriously during those years,established a partnership, prepared a consistent contract and most of our machineryand all control valves were from Metso. Metso knows our processes and this wouldhelp the advanced control implementation. It would be a smart decision, and it reallywas. Regarding the specific accomplishments of Steam Manager, he adds. For steammanagement the target was to reduce costs. The possibility to reduce steam quantityreleased into the air was identified. Based on this opportunity Metso prepared somecalculations which helped Cenibra to get a reduction in vented steam.

Ronaldo Ribeiro,Automation Specialist says, Metso knows our processes and this would help

the advanced control implementation. It would be

a smart decision, and it really was.

The first mill audit regarding Advanced Process Control (APC) solutions was carried out

in 2006. After that, the possible results and returns were calculated. In July 2008, the

mill decided to order five APC controls, one of which was Steam Manager. Before the

system was installed, Metso gathered data and studied process information concerning

the mills steam network. The operation model of the mill and its controls were studied


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to create a full-scale picture of the plants performance level in terms of energy

efficiency.

Dynamic process, modeled control

And this leg-work was well justified by the complexity and dynamics of the network.

This advanced work helped to configure the structure of the multi-variable predictive

(MPC) models which are a cornerstone of Steam Manager. The fundamental objective

of Steam Manager is to guarantee both steam quality and steam availability not too

little for the pulp mill processes and not so much that it has to be vented. Steamquality is ensured by regulating the pressures of high pressure, medium pressure and

low pressure headers at their target values of 65, 13 and 4 kgf/cm2. By stabilizing and

regulating the pressures, the high quality of process steam is obtained. Steam

availability is ensured by regulating steam balance of the steam network by ensuring

that steam production of the boilers matches to steam consumption of the turbo-

generators and the mill processes demanding process steam at any time instant.

Most of the steam at the mill is produced by three recovery boilers and the rest of the

steam is produced by two power boilers burning bio fuel. Oil burners for these power

boilers are used at start-ups and at high load situations. In addition, there is an oil

boiler available for steam outages. Two turbine-generators operate from the high

pressure header supplied by the 5 boilers. The biggest process steam consumers are

two evaporators and two continuous digesters which use medium pressure and low

pressure steam. Also, the recovery boilers require some process steam for their

operations.

The Steam Manager controls many different unit operation and valves in order to

balance supply and demand. Models take into account the interactions between several

interrelated variables, manipulated variables (MVs) which are managed to achieve

controlled variable (CV) targets in the presence of disturbance variables (DVs) which

come from a variety of sources on the supply and demand side. Figure one shows a

matrix which represents the MPC control structure at Cenibra.

The Steam Manager controls are configured in a metsoDNA system linked via OPC to

the mills existing DCS system which then carries out the loop control commands.Figure 2 show the main operator interface for the steam network.


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Figure 1: Simplified control matrix for Cenibras Steam Manager. The controlled

variables (CVs) are regulated at their set-points by managing the manipulated

variables (MVs) in the presence of disturbance variables, (DVs).

Figure 2. The main operator display page of Steam Manager in the metsoDNA system

shows the steam network layout with primary process data and control loops.

Results from day one


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Immediately after the startup in May 2009, the Steam Manager results looked very

promising and have been well documented over the following months. Steam Manager

improved the network steam and energy balance management during normal

production periods and, most importantly during disturbance periods. As shown in

figure 3 vented steam to the atmosphere has been reduced significantly.

Jlio Ribeiro, Recovery Line and Utilities Coordinator, sums up the results: Steam

Manager uses algorithms including multivariable control, as it coordinates multiple

inputs, measurements and disturbances. The commissioning phase and software

configuration involved a multidisciplinary team. The operational start-up was smooth.Results could be seen from the first day and the target of 90% reduction of blow-out

steam was reached in three months. This means 10,000 tons of steam monthly are

not being discharged to the atmosphere , which is the energy equivalent of 715 tons of

oil per month and 2, 200 fewer tons of CO2 .

Jlio Ribeiro, Recovery Line and Utilities

Coordinator Results could be seen from the first

day and the target of 90% reduction of blow-out

steam was reached in three months.

In addition, the high pressure steam pressure is more consistent as shown in Figure 4.

The stabilization of all steam pressures in the network high, medium, and low is the

backbone of the Steam Manager concept. The lower pressure must be stabilized to

provide steam at constant pressure to steam consumers. On the other hand, the high

pressure must be stabilized as it is one of the main variables that are controlled by

power boilers. If that is upset, the boiler load, and eventually the fuel consumption to

the boiler is disturbed.


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Figure 3: As a result of Steam Manager optimization, steam vented to the atmosphere

has been reduced by 90%

Figure 4: The stability of high pressure steam header supply has been improved

significantly by Steam Manager.

Operator acceptance, sustained results

The effective implementation of the Steam Manager system required some new ways

of thinking and changes in operating procedures. Jlio Ribeiro elaborates: There was

a change in the operating paradigm because the operators were used to doing it their

way. Then some new concepts were introduced into operation. Therefore some

adjustments were needed. Since the system proved to be reliable, the operators felt

comfortable with the changes. It was a new tool and it had everyones approval. At

first they were a little skeptical about it, but soon they saw it brought benefits.


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Process operator acceptance is one of the key objectives of any process management

system since they have to work with it day-to-day. When the operators fully

understand and believe in the way of operation, the results are sustained. Jairo

Ferreira, Recovery Boiler Operator, sums up his thoughts which suggest a continuing

belief in the control concept: Since I came to the department, a lot of excess steam

was being released. There was an awareness of it, but more drastic measures had to

be taken. The process instability was a limiting factor and this became the most

important goal of the Steam Manager project. This solution would help us to do what

we could not do by ourselves. When the boiler burning rate increases, the plant gets

more stable, and the energy distribution pattern is improved. What you need is to

manage all that when the process undergoes changes. In the beginning, we were notsure that steam emissions could be reduced. Then, after a closer look at the system,

we understood it better and we improved our process. Today, we have reached an

unbelievable steam reduction level that exceeded our expectations.

airo Ferreira, Recovery Boiler Operator, says, In the beginning, we were not sure

that steam emissions could be reduced. Then, after a closer look at the system, we

understood it better and we improved our process. Today, we have reached an

unbelievable steam reduction level that exceeded our expectations.

Click here and ask for more information.

Authors: Pasi Airikka and Mark Williamson
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