Overview

Lafarge Plasterboard manufactures and distributes plasterboard and associated products to the Australian market through its national distribution network of Lafarge PlastaMasta Centers. Lafarge Plasterboard is part of the global Lafarge Group, a leading global building materials supplier employing over 77,000 people and operating in over 75 countries. Lafarge Plasterboard’s manufacturing facilities are located in Matraville (Sydney) and Altona (Melbourne). The Altona site employs 60 people, and produces approximately 15 -18 million square meters of plasterboard per annum.

An energy intensive step in the process of manufacturing plasterboard is in the drying of the product. This essentially involves the use of gas fired heating to produce large volumes of heated air, which passes over the plasterboard to drive the rapid evaporation of water contained in the freshly formed plasterboard. Lafarge Plasterboard is currently considering a heat recovery upgrade for the drying process, primarily driven by the need to reduce energy costs and increased productivity.

Project Description

Current key process steps in the manufacturing of plasterboard include: plaster preparation, forming into cardboard-lined sheets, rolling/pressing, drying and packaging ready for storage and distribution. The drying process consists of a two-stage process, in Stage 1 (“Zone 1”, counter current air flow) the plasterboard is heated to 100 deg C, followed by 95 deg C in Stage 2 (“Zone 2”, co-current air flow). The plaster drying process must be carefully controlled to ensure uniform standard of product quality. The drying process operates at 100% capacity for most of the product lines produced at the Lafarge Plasterboard Altona site.

Lafarge Plasterboard implemented an innovative heat recovery technology to recover both heat and water from exhaust gases that currently vent to the outside air. Implementation of the heat recovery technology allowed the capture of energy from exhaust gases for re-use in the drying process, condensation and collection of water from the humid exhaust air and improved productivity with faster drying of the plasterboard.

Specifically, the system recovers heat from the exhaust gas from the first stage of the plaster board dryer to preheat the intake air required for the second stage of the plasterboard dryer using a heat exchanger. The supply air is drawn from outside the building, as the temperature here is lower then inside. The air passes through a filter and FD centrifugal fan, before entering the bottom side of the heat exchanger. The air travels along a 'U' path, counter-current to the exhaust stream, departing the same side at the top. The hot supply air is then ducted to the required zones; zone 1 combustion air, zone 2 combustion air and zone 2 infiltration air. Dampers were installed on all these outlets to balance the flows.

The existing zone 1 flue contained a damper which is fully open. This damper has been closed, redirecting the zone 1 exhaust through the proposed plate heat exchanger. The exhaust now enter the top of the exchanger at approximately 172 deg C, traveling along the 'I' path, leaving from the base at approximately 75 deg C. Since the stream is being cooled below its dew point, this configuration allows any water condensed in the exchanger to flow co-current with the exhaust stream, as well as a greater ease of cleaning.

Cleaning is performed by a spray supplied by mains water, set up as a deluge system at a flow of 1.5m3/min. As an indicator of particulate build-up, a differential pressure sensor indicates to the operator when the deluge system is required.

Additionally, a water collection system was installed to handle the significant volumes of water (2 tonnes per hour) which will be generated when cooling the exhaust gas from the first stage of the plasterboard dryer through this process. The collected water will be treated if necessary and reused in the process. The initial feasibility study did not include consideration of the water recover potential. This was considered as part of later works and influenced the type of heat exchanger selected.

The water recovered from the heat exchanger is collected in a condensate recovery tank. The base of the tank is sloped, so as to let any particulate matter to settle out, allowing it to be removed from the base of the tank. The tank has a level sensor to periodically pump water from the tank, supplying it back to the process water storage tank.

The development and capital implementation cost for this project was approximately $400,000 with a payback time of 4-5 years.

The project commenced in APril 2005 and was commissioned and in operation by October 2006.

Outcomes

The Lafarge Plasterboard heat recovery project resulted in a 15% reduction in the energy input required for drying, which equates to 15,000 GJ per annum saving in natural gas consumption.

The dryer operates at 100% capacity for many of the product lines produced at this site, thus limiting further production growth. The 15% reduction in dryer load will allow more product to be passed through although the percentage increase is dependent on product type. A 15% reduction in natural gas will not necessary translate to a 15% productivity improvement on all grades of product.

The greenhouse pollution reduction is expected to be 1,600 tonnes per annum, which is equivalent to removing 370 cars from Victorian roads each year. This project will also recover and recycle an estimated 6 million litres of water per annum for a cost saving of approximately $5,000 per annum.