Environmental Engineering Reference
In-Depth Information
dross, the direct labor cost associated to dross in
the current system is:
Direct Labor Cost of Current System= 0.11 $/
kg x 12,299 kg/month = 1352 $/month.
In the production cost of a battery, it is known
that the direct labor occupies a percentage of 14%,
and the overhead occupies a percentage of 26%
of the total cost. The overhead cost associated to
dross can be calculated by using these ratios and
the direct labor cost as calculated above. Knowing
that the 14% of the total cost is 1,337 $/month, it
can be calculated that the 26% of the total cost,
which corresponds to the overhead cost associated
to dross, is 2,712 $/month, as shown in Table 1.
The direct labor and overhead costs of the batch
mode are calculated similarly. In addition to the
current system, in the batch mode there is a need
of labor when collecting excess parts and rejected
grids. In the experiment, it is seen that a total of
45 minutes is spent for a production of 3 hours.
Taken into basis that the company works 24 hours
during 29 days/month, it is calculated that the
monthly labor spent for this alternative is 174
hours. Since the unit labor cost is 1.6 $/hour, the
labor cost associated to the collection of parts is:
C Labor Cost of Collecting Parts= 1.6 $/hour
x 174 hours/month = 278 $/month.
The net present values of the current system
and the batch mode are calculated for one year, as
seen in Table 1. The costs are assumed to derive
at the end of each month and the monthly inter-
est rate is taken as 1.6%. When comparing net
present values, it can be seen that the batch mode
decreases costs by 46% compared to the current
system. This alternative obviously will reduce
the quantity of lead alloy required to produce the
same amount of grid since the raw material loss in
dross will be minimized. Therefore, it will clearly
improve the productivity by reducing raw material
consumption. This alternative is also advantageous
because the waste is reduced at source. As a result,
the environmental impact of the company can be
considerably reduced by using this alternative.
Separation of Pure Lead from Dross Using
Vitaflux™:
The dross collected from the melting
pot is high in its lead (Pb) content. It is observed
that dross formed in the current system contains a
quantity of 41% of lead in a purity of 99.92%. As
mentioned before, the dross is currently collected
and sent to the recycling facility. However, if the
pure lead can be extracted from the dross inside
the facility, it will be a very beneficiary practice
since it will be possible to reuse the pure lead as
a raw material. Drossing-off fluxes are used for
this purpose in order to accumulate the oxides
and allow easy removal from the surface of the
molten lead (Brown, 1999, pp. 56-62). Specifi-
cally, there is a material called Vitaflux™, which
is used to recover the lead from dross at source
(NA Graphics, n.d.). Application of the material
is very simple. Vitaflux™ is added on the surface
of the melting pot before dross is collected. The
lead alloy begins to burn with the addition of Vi-
taflux™ and the pot is mixed until dross becomes
fine powder. At the end of the reaction, the dross
in fine powder form is accumulated on the surface
of the molten metal. Vitaflux™ has been tested
in the company and lead was recovered from the
dross successfully.
The grid casting department consists of two
melting pots. Due to the lead alloy load of the pots,
six tubes of Vitaflux™ is needed for each melting
pot every time dross is collected. Since dross is
collected once a day in the grid casting depart-
ment, one box containing a dozen of Vitaflux™
tubes is needed every day. In the calculations, it
is assumed that one year consists of 350 working
days. Therefore, about 350 boxes of Vitaflux™
are needed per year. Results from test showed
that the use of Vitaflux™ does not influence the
composition of the lead alloy in the melting pot.
Besides, when the dross collected after the use
of Vitaflux™ is analyzed in the laboratory of the
company, it was observed that the pure lead is
totally removed from the dross. Therefore, it can
be concluded that the use of Vitaflux™ creates
