During the last few month’s our Botlek depot has seen a number of changes in the technical set up of waste water treatment and energy efficiency.
Over the last few years it became increasingly clear that the capacity of the waste water treatment plant was often not sufficient to handle the waste water flows from the cleaning. Especially with high cleaning numbers regularly interventions had to be performed in order to deal with the capacity problems.
These interventions, whereby waste separately was removed from the system, created very high costs.
In the spring of 2012 it was decided to design an up rate for the waste water treatment plant in our Botlek depot. Goal was to increase the capacity of the waste water treatment plant, reduce energy consumption in a direct and an indirect way and generate our electricity partly ourselves.
The vision for this project was: “Reduce the carbon footprint of the Botlek facility”. Thus resulting in less use of energy and lower operating cost for the company.
The waste water treatment plant at Botlek is set up as a traditional Physical/ Chemical and Biological treatment. After a pre-treatment in an oil and fats separator the polluted water comes into the heart of the plant being a so called DAF unit (Dissolved Air Flotation unit).
This step in the process binds particles in the water (Coagulation) using chemicals and with air these bonded particles start to float on the surface of the water (Flotation), after which the formed sludge can be removed - see the drawing.
After that step the water is fed into a biological reactor for treatment in order to use bacteria to further clean the water. Biological mass from the bio reactor is decanted; hence water and solids are separated. Solids are collected for removal and after the water is filtered it flows into the harbor after passing through an active carbon bed. Of course water quality must meet all regulatory limits before it can go to open water in the harbor.
After board approval, design and implementation started during quarter 3 and 4 of 2012. In the up rate project the key elements were to increase massively the capacity of the DAF unit, increase also the capacity of the decanting unit and last but not least build in a heat recovery unit in order to re-use the heat from the waste water.
Also a better computer system was designed in order to have better process control with very good alarm functions. This so-called SCADA system (Supervisory Control And Data Acquisition) is like an umbrella over the basic controls of the system.
Increasing the capacity of the DAF and decanter unit has more than doubled the ability to remove sludge from the system and bio reactor. After start-up last December the systems proved to work very well. We have seen massive improvements in the process. The heat recovery unit design-basis is around 500 Kw/hr. This led to a massive reduction of the use of steam because we are now able to pre-heat our feed water for the cleaning.
This not only gives financial savings, but also the carbon footprint of the Botlek impressively improved.
To illustrate this:
- on a per 14 hour day basis with the capacity of 500 KW we now can re-use 25.200 Mega joule per day, which equals pre-heat 200 m3 of feed water from 12 to 42 °C.
- Because a lot of steam is not used anymore, calculations show that we have 350 tons of CO2 emission less on annual basis. This equals 174 medium cars less on the road for example.
- Based on a number of design details electricity consumption is reduced with about 28% in total.
Together with this project it was decided to take over the windmill we have on the depot. The mill was owned by Eneco and feeds electricity into the national grid. As per November last year the take over process started. Goal is to produce a part of our electricity ourselves and feed only the surplus into the grid and vice versa in case there is no wind.
So with these initiatives we bring the Botlek depot back up to technical standard and at the same time we contribute to the environment considerably.
Because we have to run a company it turned out to be very rewarding to see that we also can save a lot of costs for the operation.
Business Unit Manager Depots.