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What are CO2 emissions from abrasives (corundum, garnet and Grittal)?

CO2 (kg)CED (MJ)Waste (kg)Costs per hour (€)
Grittal9,6143,41,99,2
Corundum61,0981,654,528,9
Garnet Sand45,8760,6130,653,2
Table 1 CO2 emissions, waste and energy demand for abrasives (whole chain)

For CO2 and Cumalative energy demand (CED), it applies to corundum and garnet sand that the abrasive itself makes the largest contribution, while the influence of the use and waste phase is much smaller. In the case of Grittal, the greatest impacts on CO2 and CED occur in the use phase. In terms of final waste, for Grittal and corundum about half of the waste is generated in the production of the abrasive, while the other half is generated when the abrasive is dumped. For garnet sand, however, landfilling is the main contributor to total waste. In terms of costs, for all blasting media, the purchase of the abrasive itself is the largest contributor, while the influence of the use and waste phase is much smaller.

One of the important differences between Grittal on the one hand and corundum and garnet sand on the other is The production of Grittal uses a lot of ferrochromium. Given the growing attention attention to the depletion of metal reserves, it is better to recycle the blast dust of Grittal (which consists largely of ferrochromium) or look for other surface preparation alternatives.

Background

Many surfaces that we see in everyday life have a coating that makes the material last longer and performs its function better. Cars, trains, bridges, pipes, etc. are all coated, against rust. They are all provided with coatings, but before a coating can be applied to to a surface, a number of other processes are required, including blasting.

With the emerging awaraness that we need to decrease carbon dioxide emissions along the whole chain of steel protection, the questions concerning the sustainability of grit blasting are increasing.

In the surface treatment industry, corundum and garnet sand, among others, are currently used as abrasives. However, a number of companies are using a new alternative abrasives such as Grittal, which has a number of advantages over regular abrasives. For example In the usage phase, besides the energy savings, there are also health and safety improvements to be made, as blasting is

health and safety, as blasting with Grittal, for example, generates much less dust than regular blasting. However, due to its properties and financial considerations, it is most logical to assume that Grittal replaces corundum or garnet sand.

Within this comparison we are aware that corundum and garnet sand, a large number of other abrasives are also used, such as steel grit, glass beads, ceramic beads, etc. Because of the properties of Grittal and financial considerations, however, it is most logical to use Grittal.

Methodology of this comparison

By combining the inputs and outputs in each chain with the environmental effects of those inputs and outputs, the environmental effects of the chains of Grittal, corundum and garnet sand were calculated. In addition, the total operating costs of using the various abrasives have also been calculated.

The sources used are also listed with the impacts. In many cases, for the background data, the Ecoinvent database was used. In addition, use was made of chain studies conducted earlier, information from the manufacturer/supplier and information from the end-user.

Resource usage during the production of abrasives

The following table provides an overview of the required raw materials and other resources for the production of Grittal, Corundum and Garnet Sand. Within this data both the productions, the transportation have been taken into account.

Garnet sand (kg)Aluminiumoxide (kg)Scrap Iron (kg)Ferrochromium (kg)Hydrogen (kg)Crush-ingElectricity (kwh)Transport (kg.km)
Grittal0,570,481,8E-051,00,186000
Corun-dum1,024800
Garnet sand1,014200
Table 2 Quantity of raw materials and resources required to produce 1 kg abrasive

Ferrochrome, which is used for the production of Grittal, is mostly produced in South Africa. Therefore, a transport distance of 11369 km by sea (Cape Town-Rotterdam3) times 0.48 kg was assumed, i.e. 5491 kg*km. A further 240 km from the port of Rotterdam to the production site was also assumed to the production site  and an additional 160 km from the production site to the distributor iand 300 km from the distributor to the end user, all three by truck.

Alumina is mostly produced in produced in Australia (500 km truck transport in Australia, 17800 km sea transport from Fremantle to Rotterdam, whereas garnet sand is mostly extracted in India (500 km train transport in India, 13500 km sea transport from Chennai to Rotterdam). For all abrasives we assumewe assume that they are packed per 25 kg in a plastic packaging (PVC) of 100 grams. Based on the figures in Table 1 and the corresponding environmental impacts, the environmental impact of the production of 1 kg of Grittal, Corundum and Garnet sand has been calculated.

CO2 (kg) CED (MJ) Waste (kg) Price per kg (€)
Grittal3,442,60,88,25
Corundum1,625,90,80,8
Garnet sand0,34,10,00,3
Table 3 CO2 emissions, Energy usage and wast to produce 1 kg of abrasive

As the net quantities required for use differ, for a better picture also the net abrasive consumption per hour and corresponding effects and costs are shown (Table 3).  The difference between Table 3 and Table 4 is thus in the unit: the figures in Table 2 are for the production of 1 kg of abrasive, whereas the figures in Table 3 are for the production of the quantity of abrasive required for 1 hour of blasting. For example, the cost of Grittal is 8,25 €/kg, whereas corundum costs about 0,80 €/kg (Table 2). The net consumption of Grittal is 1.0 kg/hour blasting, which brings the cost for the purchase of the abrasive to €8.25 per hour of blasting.  The net consumption of corundum is 30,2 kg/hour blasting, with which the cost of the abrasive purchase amounts to € 24,20 per hour blasting.

Usage (kg/hr) CO2 (kg) CED (MJ) Waste (kg) Price per kg (€)
Grittal1,03,443,00,88,3
Corundum30,248,9781,424,124,2
Garnet Sand128,932,3532,11,538,7
Table 4 CO2 Emissions corrected with net usage per hour

In this article we explain how you can calculate the net usage of abrasive medium per unit: https://www.corrosionalliance.com/prep/how-much-abrasives-do-you-need-for-a-grit-blasting-project/

Grit blasting emissions and resource usage

In addition to abrasives, blasting requires electricity to drive the compressor and to extract dust. Also hoses, nozzles and filters are needed. When blasting with Grittal, less dust is generated than when blasting with corundum or garnet sand. Therefore, less electricity is less electricity is needed for dust extraction. In a typical hall, blasting with Grittal requires 7.5 kW for suction, while corundum and garnet sand require 15 kW6. In order to spray the abrasive a compressor is needed, which consumes about 800W7, regardless of the type of abrasive used.

Hoses and nozzles with Grittal have a lifetime of approximately one year. When using sand, hoses have a lifetime of about 4 months, and nozzles 6 months. Filters have a life of at least 5 years, and as far as we know, this does not depend on the type of abrasive used. The quantities of electricity, hoses, nozzles and filters needed for 1 hour blasting at 5 bar with a 12 mm nozzle are shown in the following. By multiplying these quantities by the environmental effects and costs, the environmental effects and direct costs per hour blasting can be calculated (Table 5).

InputGrittal CorundumGarnet Sand
Electricity (ventilation) kWh7,51515
Electricity (blasting) kWh 0,820,820,82
Hose0,00060,00170,0017
Nozzles0,0060,00110,0011
Filter0,00010,00010,0001
Table 5 Resource usage during grit blasting process

It can clearly be seen that the largest part of the resource usage is caused by the electricity needed for the ventilation

CO2 (kg) CED (MJ) Waste (kg) Price per kg (€)
Grittal6,1100,20,10,8
Corundum11,7191,50,21,7
Garnet sand11,7191,50,21,7
Table 6 CO2 emissions, Energy usage during grit blasting process

Waste

During the blasting process, part of the abrasive becomes dust. This dust is collected in big bags. When the big bag is full, it is transported to the waste disposal site for disposal. For the disposal of 1 ton of blasting grit, 1.43 kg of polypropylene is needed (the big bag), and 60 MJ diesel (transport). The average transport distance to the dumping site is 35 km10. In combination with the environmental effects of this (see Annex 1), the environmental impact of the dumping of In combination with these environmental effects, the environmental impact of the dumping of blasting grit can be calculated. Table 6 shows the environmental impact of the landfilling of 1 kg of blasting grit. This is irrespective of the exact type of blasting grit.

CO2 (kg)CED (MJ)Waste (kg)Costs per hour (€)
Waste grit0,00,31,00,1
Table 7 Effects of waste

Integrated environmental assesment of different abrasives

Based on the environmental impact in the raw materials phase, the use phase and the waste phase, the total environmental impact is calculated. These total environmental effects of the use of Grittal, corundum and garnet sand per hour blasting are shown in Table . (CED) per hour of blasting, broken down by abrasive, use and waste. From this it is clear that for corundum and garnet sand, the abrasive itself contributes most to the total CED, while the use and waste phase play a much smaller role. For Grittal, the use itself contributes the largest contribution to the total CED.

CO2 (kg)CED (MJ)Waste (kg)Costs per hour (€)
Grittal9,6143,41,99,2
Corundum61,0981,654,528,9
Garnet Sand45,8760,6130,653,2
Table 8 Integrated sustainability assesment abrasives

The remarkable thing is therefore that Grittal – if we look at the total operating costs – is cheaper than than corundum and garnet sand, while the price per kg is about ten times higher than that of corundum and garnet sand. This has to do with two things. Firstly, for one hour of blasting, much less Grittal is net needed than corundum or garnet sand , so the costs are lower. Secondly, blasting with Grittal generates much less waste than blasting with corundum or garnet sand, so that the costs of waste disposal are also considerably lower.

All in all, the use of Grittal is thus cheaper than the use of corundum and garnet sand and contributes to reduce emisions and energy demand.

Source: This article is based on a chain comparison that was executed by MWH global. This asignment was performed under contract of the Dutch government.

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