Hot repairs and rebuilds I 

Partial rebuild of a glass melting 

furnace 

The decision to partially rather than completely rebuild a glass 

melting furnace towards the end of its campaign life is dependent 

on several factors, including costs and projected sales 

requirements. Michael Horsfield*, Managing Director of glass 

plant engineering company Dismatec, reflects on the process 

chain requirements for a partial rebuild. 

T

owards the end ot the designed or 

extended campaign life of a glass 

melting furnace, the question 

commonly asked by the company's 

senior management is: 'Do we need to 

totally or partially rebuild the furnace 

and what campaign life are we looking 

for after the rebuild?' Significant factors 

affect the decision making process and 

ultimately the final decision. These 

include: Current, new and future 

technologies; marketing strategies; 

production scheduling to meet current 

and projected sales; what is happening 

m the market; capital cost of the project; 

payback period; and commercial aspects. 

For the purpose of this article, the 

decisiOn made is to partially rebuild the 

furnace for a campaign life of three 

years prior to a major overall, including 

a furnace design change and the 

introduction of up-to-date technology 

to meet future production and sales 

reqmrements. 

Decision making 

This decision process should start at 

least 12 months in advance of any 

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 

of the furnace to be addressed for the 

purpose of determining the major part 

of the scope of work is the refractory 

structure. It is normal for the supportmg 

and bracing steelwork to be re-used, with 

the exception of any items that have 

experienced 'heat-attack' or are seen to 

be potentially structurally instable. The 

furnace service systems, including fuel, 

Typ1cal locat1on of the tapp1ng hole and dra1n1ng 

of the furnace 

coohng and control, normally remain in 

their entity with an amount of 

maintenance work being included for 

each system and the replacement of 

thermocouples and electrodes of an 

electric boost system if installed. 

To make a total and comprehensive 

decision on the required scope of work 

for the refractory structure, while the 

furnace is operational, is very difficult. 

However, from the views of expenenced 

factory personnel together with the use 

of available external services such as 

visual and thermography audits, a good 

assessment of requirement can be 

concluded for commercial budgeting 

and the initial bills of material purposes. 

Because the scope of work is an 

assessment and it is very likely that 

items in addition to those identified 

will be required, an amount of money 

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 of the 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 of the furnace. 

Therefore it is important to have all the 

existing refractory specifications to 

hand for reference when selecting the 

required new refractories. 

It is 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 of time 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 may have 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 of concentration 

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. 

continued >> 

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I Hot repairs and rebuilds 

Depending on the actual condition 

and results of a risk assessment of the 

furnace refractory structure, it ts not 

uncommon for parts of the melting end 

sidewalls, throat, superstructure, ports, 

regenerators and regenerator packing 

together with the distributor and forehearths to remain in position and be reused for the new furnace campaign life. 

The scope of work follows a sequence 

of events identified on a Gantt chart or 

similar project tool to aid with the 

planning, logistics and management of 

the project. By using the Gantt chart, 

progress of work can be tracked throughout the rebuild period and any conflicts 

of work disciplines, material logistic 

problems and problems wtth meeting 

milestone and target dates can be identified at an early stage, therefore minimising the nsk of unforeseen problems and 

over-runnmg on the project programme. 

The given scope of work 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, 

if chosen to be included, should ideally 

arrive on site prior to the tap and drain 

of the 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 

programme being 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 of construction 

methods and build sequence. 

Furnace tap and drain 

A tapping 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 'tapping bay' by 

means of chutes, then transferred to a 

clean storage area near to the cullet bay 

so that it can be mixed with the cullet, 

if required, for the 'ftll-on' process 

during the pre-heating of the rebuilt 

furnace structure. During the draining 

process, the furnace temperature is 

regulated to meet the temperature and 

flowing characteristics of the molten 

glass exiting via the tapping hole. 

The obJeCtive of the draining process 

is to leave as little glass in the furnace 

as possible (normally S0-70mm). This 

helps to reduce the amount of work 

required during the dismantling process 

of the existing furnace refractory 

structure and the amount of glass to be 

disposed of to landfill or another 

source. Generally, this glass is disposed 

of to landfill due to refractory materials 

being present when removed from the 

bottom of the furnace. 

Also, depending on the type of glass 

and its composition, the remaining 

glass left to be disposed of may fall into 

the category of hazardous waste, which 

is more difficult to dispose of to the 

correct environmentallegislatwn. 

Controlled cool-down 

If prominent 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 to cool down the existing 

furnace, after completion of the 

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 to be built. 

The controlled cool-down is carried 

out using specialist heating equipment 

to reduce the temperature of the 

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 draining process 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 of the 

existing furnace refractory structure and 

any areas of supporting steelwork that 

may have experienced 'heat attack'. 

The results of the cold inspection can 

be checked against the partial rebwld 

scope of work and any additional work 

introduced into a final scope of work 

programme. 

continued » 

Internal wear of the melting end c1own 
Execution 

Work commences duectly after the 

completion of the cold inspection with 

the dismantling of the 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 of pipework, ductwork, 

steelwork, electrical Items and control 

monitoring equipment to allow access 

to the refractory structure and prevent 

any possible 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 of the refractory commences, 

with care being taken at all interface 

positiOns of the 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 of injury, a full 

and comprehensive method statement 

and risk assessment for all work tasks to 

be executed, together with any COSHH 

data, should be prepared in advance of 

work commencing and accepted by the 

site health and safety management, with 

copies given to a COM co-ordmator. All 

personnel assigned to work on any task 

should have read and understood these 

prior to commencmg any work. 

To adopt a high level of health and 

safety, all partial rebuild work should be 

carried out to the current COM 

regulations or equivalent, depending on 

the country where the work is to be 

earned out. 

A well-executed rebuild reflects on 

good project management, includmg 

site and health and safety management. 

Hot-repairs and rebuilds I 

This is a key factor to problem solving 

during the 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 construction phase is 

complete, the refractory structure and 

systems are inspected and checked, the 

furnace pre-heat is started to bring the 

furnace up to operating temperature 

and ready for producing glass on a 

gradual temperature gradient basis. This 

rs done with the use of specialist heatmg 

equipment and a pre-heat schedule. 

Withm the schedule are timings for the 

introduction of the main furnace 

burners, cullet and batch fill-on. When 

the furnace is full of glass and the 

production machines are ready the new 

furnace campaign life can begin. • 

*Michael Horsfield, 

Managing Director, Dismatec, UK. 

Email: intoradismatecglassplant.com 

Web: www.dismatecglassplant.com