Environment industries archive
Key departmental publications, e.g. annual reports, budget papers and program guidelines are available in our online archive.
Much of the material listed on these archived web pages has been superseded, or served a particular purpose at a particular time. It may contain references to activities or policies that have no current application. Many archived documents may link to web pages that have moved or no longer exist, or may refer to other documents that are no longer available.
|Objective of this Session||To be introduced to the detailed study, discuss issues with data quality, and introduce quantitative usage maps as a tool for data collection|
|The following topic will be covered in this session|
|Data Validation - Mass Balance|
Calculating a mass balance is probably the most powerful of the tools for validating data. It is used with usage maps and input/output diagrams, and is based on the knowledge that whatever is put in to a process or unit process must emerge from that process either as useable product or else as waste of some sort.
The goal of cleaner production is that all input materials are output as the desired product. The more common reality is that input materials are output as the product, and also as a variety of solid, liquid and gaseous wastes.
Mass balances can be used in one of two ways. The most common way is with usage maps. The total input or waste is usually fairly easily established. What is more difficult to establish is the breakdown of this total figure on the other side of the usage map. Of course, the total of each side must be equal (mass can't disappear!). If it doesn't balance, then data validation techniques can be used to investigate the differences.
The second way that mass balance is used is with input/output diagrams. Quantitative data can be applied to these diagrams to get an estimate of waste from the unit process. For example, if 100 kg/day of steel goes into one or more unit processes, and 80 kg/day comes out as product, then the remaining 20 kg must be waste.
In an electroplating plant, such as described in the Session 3 case study, the following data of average weekly results were recorded.
Nickel anodes added: 4 kg
Nickel deposited onto steel shafts: 7 kg
Loss of nickel from 2000 litre solution: 2 g/l (= 4 kg).
(This was added each week as nickel salts concentrate)
How much nickel was lost per week as drag-out from the nickel tank?
A quantitative usage map is constructed, as shown in Figure 20.1, and the mass balance calculation provides the answer.
|4 kg anodes|
|plus 2g/l x 2000 l = 4 kg||à||Deposited onto steel shafts||7 kg|
|Total of 8 kg per week nickel added||à||Dragout losses||unknown|
|Therefore||Dragout losses =||1 kg (12.5 litre of 80g/l nickel solution|
|8 kg in||Total quantity of nickel per week||8 kg out|
Figure 20.1: Use of Mass Balance to calculate dragout losses
Objective: to demonstrate that available data is not always complete, and to use a mass balance calculation to fill the data gaps.
In the spray painting case study used in Session 3, the data on solvent usage which led to process changes would typically not be have been complete before the cleaner production program was developed.
The data which might have been available included:
Data on solvent used for washing spray guns would not normally be available, and loss of solvent as spillage and solvent used in general cleaning in the paint spraying area would also not be available.
Brainstorm the question: how do you collect or estimate this needed data. The total quantity of solvent consumed by processes other than as mixing paint is the difference between overall consumption and the amount used in mixing paints.
Objective: to gain experience in using mass balance calculations to find unknown quantities in the input or output of a process.
At O'Shaugnessy and McFarlane Chemicals Manufacturing plant, during November 1998, the water meter reading showed 15 kL of total water consumption on the site.
The trade waste effluent for the same month was 5 kL. The average water content of the products is 50% by weight. During November, 16 tonne of products were manufactured. Using Dept of Labour and Industry standard ratios of staff numbers to water usage, the water used for "domestic" purposes was estimated as 2 kL.