### Hot repairs and rebuilds

# I Partial rebuild ofaglassmelting 

# furnace

The decision to partially rather than completelyrebuild a glass meltingfurnace towards the end ofits campaign life is dependent on several factors, including costs and projected sales requirements. Michael Horsfield*, Managing Director ofglass plant engineeringcompany Dismatec, reflects on the process chain requirements for apartial rebuild. 

# T owards the end ot the designed or extended campaign life ofa glass meltingfurnace, the question commonlyasked by the company's seniormanagement is: 'Dowe need to totally orpartially rebuild the furnace and what campaign life are we looking for after the rebuild?' Significant factors affect thedecision makingprocess and ultimately the final decision. These include: Current, new and future technologies; marketing strategies; production schedulingto meet current and projected sales; what is happening m the market; capital cost ofthe project; paybackperiod; andcommercial aspects.

For the purpose ofthis article, the decisiOn made is to partially rebuild the furnace for a campaign life ofthree years prior to a major overall, including a furnace design change and the introduction ofup-to-date technology to meet future production and sales reqmrements. 

### Decision making This decision process should start at least 12 months in advance ofany proposed rebuild date in order to determine commercial aspects, proJected marketing and sales requirements and to meet materials and equipment delivery lead times.

For a partial rebuild, the main section ofthe furnace to be addressed for the purpose ofdeterminingthemajorpart ofthe scope ofwork is the refractory structure. It is normal for the supportmg and bracing steelwork to be re-used, with the exception ofany items that have experienced 'heat-attack' or are seen to be potentially structurallyinstable. The furnace service systems, including fuel, Typ1cal locat1on of the tapp1ng hole and dra1n1ng of the furnace coohng and control, normallyremain in theirentitywith an amount of maintenance work being included for each system and thereplacement of thermocouples and electrodes ofan electricboost system ifinstalled.

To make a total and comprehensive decision on the required scope ofwork for the refractory structure, while the furnace is operational, is very difficult. However, from the views ofexpenenced factory personnel together with the use ofavailable external services such as visual and thermography audits, a good assessment ofrequirement can be concluded for commercial budgeting and the initial bills ofmaterial purposes.

Because the scope ofworkis an assessment and itis very likelythat items in addition to those identified will be required, an amount ofmoney should be included for these in the commercial budget. 

### Materials selection For partial rebuilds it is very Important to select the correct type and grade ot refractory that is 'fit for purpose' for each area ofthe furnace refractory structure.

The new refractories have to be compatible with the existing so as not to create a wear or corrosive reactiOn during the operation ofthe furnace. Therefore it is important to have all the existing refractory specifications to hand for reference when selecting the required new refractories.

Itis not uncommon for each factory department involved in the partial rebmld to mclude a 'wish list' (a list of items to help rectify problems experienced over a period oftime and spare parts to help with ongoing maintenance throughout a furnace campaign life) while determining a scope of work for the rebuild. A rebuild time is seen as an opportunity to obtain items that mayhave been rejected dunng the existmg campaign period. 

### Scope of work For a partial rebuild furnace campaign life of three years pnor to a maJor overall, the main area ofconcentration is the furnace melting end. All other areas are assessed for present condition, problems expenenced throughout the existing campaign life period, potential problems that may be encountered during the future campaign life period, future maintenance requirements and risks against decisions made.

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# I Hot repairs and rebuilds

Depending on the actual condition and results ofa risk assessment ofthe furnace refractory structure, it ts not
uncommon for parts ofthe melting end sidewalls, throat, superstructure, ports, regenerators andregenerator packing together withthe distributor and forehearths to remain inposition andbe reused for the newfurnace campaignlife.

The scope ofwork follows a sequence ofevents identified on a Ganttchart or similarproject tool to aid with the planning, logistics and management of the project. By usingthe Ganttchart, progress ofwork canbe tracked throughout the rebuild period and anyconflicts ofwork disciplines, material logistic problems and problems wtth meeting milestone and target dates can be identified at anearly stage, therefore minimisingthe nsk ofunforeseen problems and over-runnmg on the projectprogramme.

The given scope ofwork for the rebuild follows a sequence of events or tasks in order for work to be carried out correctly and logically. Work carried out in the UK is under the current Construction Design and Management (COM) regulations and similar in

overseas countries.

Refractory materials and equipment, ifchosen to be included, should ideally arrive on site prior to the tap and drain ofthe existing furnace. This ensures that the partial rebuild can start on the chosen date, without the concern of watting for materials to be delivered and the possibility of the construction programmebeing disrupted.

Internal weal of a melt,ng end sold1er block 

# /

Materials should be checked against the order upon delivery and stored to meet the requ1rements ofconstruction methods and build sequence. 

### Furnace tap and drain Atapping hole is drilled at a designated location m the melting end and from this the existing furnace is drained of glass using speciahst equipment. The glass is directed into a 'tappingbay' by

means ofchutes, thentransferred to a clean storage area near to the cullet bay

so that it canbe mixed withthe cullet, ifrequired, for the 'ftll-on' process during the pre-heating ofthe rebuilt furnace structure. Duringthe draining process, the furnace temperature is regulated to meet the temperature and flowing characteristics ofthe molten glass exiting via the tapping hole.

The obJeCtive ofthe draining process is to leave as little glass in the furnace

as possible (normally S0-70mm). This helps to reduce the amount ofwork required during the dismantling process ofthe existing furnace refractory structure andthe amount of glass to be disposed ofto landfill or another

source. Generally, this glass is disposed ofto landfill due to refractory materials beingpresentwhen removed from the bottom ofthe furnace.

Also, depending on the type ofglass and its composition, the remaining glass left to be disposed ofmay fall into the category of hazardous waste, which is more difficult to dispose ofto the correct environmentallegislatwn. 

### Controlled cool-down Ifprominent sections of the existing furnace refractory structure, including crowns, soldier blocks, throat, superstructure, regenerator structure and forehearths are to remain in situ for the next campaign period it is normal tocool down the existing furnace, after completion ofthe draining process, m a controlled way. This ensures that structural stability is maintained and that any given structure remaining is in the correct position for new structures or part structures tobe built.

The controlled cool-down is carried
out using specialist heating equipment

to reduce the temperature ofthe furnace on a gradual scheduled basis. Working to a cool-down temperature schedule, the contraction of the furnace refractones is regulated from the end of the drainingprocess to room temperature.

After the furnace has been drained of glass and the controlled cool-down complete, it is normal to inspect the internal areas of the existing furnace, to

assess the actual condition ofthe existing furnace refractory structure and any areas of supporting steelwork that may have experienced 'heat attack'.

The results ofthe cold inspection can be checked against the partial rebwld scope ofwork and any additional work introduced into a final scope ofwork programme.
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Internalwear of the melting end c1own

### Execution Work commences duectly after the completion ofthe cold inspection with the dismantling ofthe existing furnace refractory structure to be replaced. Dismantling is carried out in a controlled and careful way so as not to remove more than is necessary. All the removed refractory materials are disposed of m the correct way following current envrronmentallegislation, methods and requirements.

During the refractory dismantling process it may be necessary to remove an amount ofpipework, ductwork, steelwork, electrical Items and control monitoring equipment to allow access to the refractory structure andprevent anypossible damage to equipment.

This work is carried out in sequence with the refractory dismantling process. Also, if any work IS required on the steelwork structure thrs b done in the same way.

After the dismantling phase, the buildmg ofthe refractory commences, with care being taken at all interface positiOns ofthe existing refractory structure m order to create a good and clean transition. Upon completiOn of the refractory rebuild, dll the removed pipework, ductwork, steelwork, electncal items and control monitoring equipment are replaced at the correct time ready for the furnace pre-heat. 

### Health and safety In order to optimise health and safety and minimise the risk ofinjury, a full and comprehensivemethod statement andrisk assessment for all work tasks to be executed, together with anyCOSHH data, shouldbe prepared in advance of work commencingand accepted by the site health and safety management, with copies given to a COM co-ordmator. All personnel assigned to work on anytask should have read and understood these priorto commencmganywork.

To adopt a high level ofhealth and safety, all partial rebuild work shouldbe carried out to the current COM regulations orequivalent, depending on the country where the work is to be earned out.

Awell-executed rebuild reflects on goodproject management, includmg site and health and safety management. 

### Hot-repairs and rebuilds

# I

This is a key factor to problem solving duringthe rebuild period, maintaining workforce teamwork and communication together With following the reburld schedule to achieve the final date set down on the construction programme and keeping the customer informed on the project at all required stages.

After the constructionphase is complete, the refractory structure and systems are inspected and checked, the furnace pre-heat is started to bringthe furnace up to operating temperature and ready for producingglass on a gradual temperature gradient basis. This rs done with the use ofspecialist heatmg equipment and a pre-heat schedule. Withm the schedule are timings for the introduction ofthe main furnace burners, cullet and batch fill-on. When the furnace is full ofglass and the production machines are readythe new furnace campaign life can begin. • *Michael Horsfield, Managing Director, Dismatec, UK. Email: intoradismatecglassplant.com Web: www.dismatecglassplant.com