Comparison of carbon emission calculations for bulk cement and bagged cement

The core of comparing bulk cement and bagged cement lies in the "differences in packaging and the resulting logistics and handling efficiency." The following is a detailed, structured comparative analysis. The core conclusion is that, over the entire life cycle, bulk cement has significantly lower carbon emissions than bagged cement. Its main advantages lie in the "production and disposal of packaging materials" and "logistics handling efficiency." However, in the core production stage (clinker calcination), carbon emissions are the same for both.

We adopt a "cradle-to-grave" life cycle assessment (LCA) method, focusing on comparing the different stages.

System Boundaries: Cement production process (A1-A3) + Transportation to construction site (A4) + End-of-life stage (C).

Note: Carbon emissions from the cement production process (A1-A3) are "completely identical" for both bulk and bagged cement because packaging occurs after production is complete. Therefore, the focus of the comparison is on stages A4 and C.

II. Quantitative Calculation Comparison (with Examples)

Assume the core process emissions (A1-A3) of producing 1 ton of cement (clinker coefficient 0.70) are 0.587 tons of CO₂e.

(Consistent with the calculations in the next section). We calculate the additional carbon emissions from packaging and transportation.

1. Carbon Emissions from Packaging Production

Bagged Cement: Typically, each ton of cement requires 20 50kg plastic woven bags.

Each plastic woven bag weighs approximately 0.125kg.

The carbon emission factor for producing 1kg of plastic (PP/PE) is approximately 2.0kg CO₂e/kg.

Calculation: 20 bags/ton * 0.125kg/bag * 2.0kg CO₂e/kg = 5.0kg CO₂e/ton of cement. This is equivalent to an additional 0.005 tons of CO₂e/ton of cement in carbon emissions.

Bulk Cement: This emission is almost zero.

Assuming a transportation distance of 100 km, using heavy-duty diesel trucks (emission factor: 0.1 kg CO₂e/ton·km).

Bulk Cement: Specialized bulk trucks can carry 40 tons.

Calculation: 100 km * 1 ton * 0.1 kg CO₂e/ton·km / 40-ton load = 0.25 kg CO₂e/ton of cement.

(This calculation allocates emissions to each ton of cement.)

Bagged Cement: Due to packaging and loading/unloading limitations, ordinary trucks can only carry 20 tons. More importantly, the return trip is empty, and the carbon emissions from the empty load need to be allocated to the cargo.

Simplified Calculation:

Outbound Full-Load Emissions: 100km * 1 ton * 0.1kg CO₂e/ton·km / 20 tons = 0.5kg CO₂e/ton of cement

Return Empty-Load Emissions (estimated based on 50% energy consumption): 100 km * 1 ton * (0.1kg CO₂e/ton·km * 50%) / 20 tons = 0.25kg CO₂e/ton of cement

Total Transportation Emissions: 0.5 + 0.25 = 0.75kg CO₂e/ton of cement

Bagged Cement: Assume 3% waste (dampness, damaged packaging).

Calculation: 0.587 tons CO₂e/ton of cement * 3% = 0.0176 tons CO₂e/ton of cement = 17.6 kg CO₂e/ton of cement

(This means you are paying 100% of the carbon emissions for each ton of cement, but only using 97% of the product.) Bulk cement: This waste is almost zero.

4. Carbon emissions from packaging waste disposal

Bagged cement: Assuming all plastic bags are incinerated, the incineration emission factor is approximately 1.5 kg CO₂e/kg plastic. Calculation: 20 bags/ton * 0.125 kg/bag * 1.5 kg CO₂e/kg = 3.75 kg CO₂e/ton of cement

Bulk cement: This emission is 0.