LCA Food 2012 in Saint Malo, France! - Manifestations et colloques ...

PARALLEL SESSION 6A: TOOLS AND DATABASES 8 th Int. Conference on LCA in the
Agri-Food Sector, 1-4 Oct 2012
At the gtg level, other processes with significant energy use and significant byproduct formation are diethanolamine,
ethylene, white phosphorus, chlorine, and sodium hydroxide. In this rollup, chlorine and sodium
hydroxide are used in quantities similar to their production rates, and so, the impact of allocation
choice is minor. The ethylene and diethanol amine gtgs each produce products with similar utility and
chemical properties. White phosphorus has a fairly small energy contribution, however, the allocation to
lower value products is high. Thus, the phosphorus allocation may be important in the result.
The total process energy is 88.1 MJ/kg glyphosate. Process energies are scaled to account for cradle to
gate delivery of fuel and again scaled to account for energy generation efficiencies. The total high heat value
(HHV) of fuels used ctg is 148 MJ/kg glyphosate. Using this presentation, it is very easy to apply alternative
energy production models and update these data as energy supplies change.
The process and natural resource energies for glyphosate production are summarized in Fig. 2.
In this view, energies for commodity chemicals are shown as ctg values. The energy profile dominated by
the glyphosate gtg, which uses 63 MJ of the total 88 MJ of process energy/kg glyphosate. We can learn
more about the energy use, potential variability between manufacturers, and potential for improvement by
looking more closely at the glyphosate gtg. The full glyphosate gtg report contains a detailed description of
the process, a process flow diagram, and Tables detailing mass and energy flows at the unit operation level.
This document can be obtained by contacting the article authors. The glyphosate process takes place in a
dilute aqueous solution, and about 80% of the energy use in the glyphosate gtg is for evaporation of the water.
Based on most of the patent data (US 6,921,84; US 7,799,571; US 5,962,729; US 3,969,398), the water
use ratio (kg water/kg PMIDA) was 10:1 to 50:1. In our gtg model, the water use was 36 kg/kg PMIDA.
Evaporation of water is an energy intensive process, and this energy can be reduced dramatically by using
multi-effect evaporators. These units split the evaporation into multiple stages and utilise the steam from
each stage as an energy supply for successive stages. An economic tradeoff between capital cost and operating
(energy) costs favours more evaporation steps in larger processes. In the glyphosate model, a single effect
evaporator was used. Thus some industrial plants may achieve significantly lower energy use by increasing
reactor concentrations and using multiple effect evaporators.
Feedstock use of fossil fuels can be seen in Fig. 1. Natural gas is used to make formaldehyde and ammonia,
petroleum is used to make ethylene oxide, and coal is used to make metallurgical coke for phosphorus
production. Using high heat values of 29 MJ/kg for coal, 54 MJ/kg for gas, and 45 MJ/kg for oil, the total
feedstock energy is 33,000 MJ/Mt glyphosate. Thus, the cumulative energy demand is 181,000 MJ/Mt glyphosate.
Two allocation choices in the glyphosate supply chain are in the ammonia gtg, which produces CO2, and
the white phosphorus gtg, which produces slag and fuel gas. We tested the impact of these allocation
choices by setting the allocation to ammonia and phosphorus to 1. Thus, no inventories were allocated to
CO2, slag, or fuel gases. In that case, the process energy, nre, and cumulative energy demands were 97, 187,
and 235 MJ/kg glyphosate.
Table 2. Cradle to gate energies for 1000 kg glyphosate.
Chemicals Mass By-products
Allocation
factor
Energy with allocation, MJ/1000kg glyphosate
Dow-
Direct use Trans- Potential Total net
kg / 1000 kg glyphosate kg / kg chemical Electricity therm Steam of fuel port* recovery energy
glyphosate 1,000 1.00 500 0 7.72E+04 0 440 -1.48E+04 6.33E+04
Oxygen
0.0553 kg Argon; 3.26 kg
641 Nitrogen; 0.231 403 0 0 0 0 -2.88 401
PMIDA 1,422 1.00 25.1 0 2,172 0 626 -745 2,079
DSIDA in 37pct sol 1,186
1.25 kg Ethanol Amine;
0.235 kg Triethanol amine;
0.0141 kg triethanol amine, 85
1.00 340 0 1,570 0 0 -7,323 -5,413
diethanol amine 765 wt pct; 0.400 149 0 3,094 0 337 -1,043 2,536
Ammonia 169 1.18 kg CO2;
3.00E-03 kg Butane; 0.0400
kg Ethane; 7.00E-03 kg LPG
condensate; 0.0100 kg
0.459 126 0 738 642 74.5 -606 976
Natural gas 205 Propane; 0.943 0 0 0 698 0 0 698
nitrogen from air 65.1 0.358 kg oxygen from air; 0.736 0 0 0 0 0 0 0
oxygen from air 882 2.79 kg nitrogen from air; 0.264 0 0 0 0 0 0 0
Water for rxn 1,005 1.00 0.809 0 0 0 0 0 0.809
Ethylene oxide 603
0.480 kg C4 stream; 0.0881
kg fuel oil; 0.0484 kg
Hydrogen; 0.569 kg CH4;
0.634 kg Propylene; 1.03 kg
1.00 1,169 0 22.5 0 265 -3,426 -1,970
Ethylene 452 pyrolysis gas;
1.55 kg heavy gas oil, from
distillation; 0.644 kg
kerosene, from distillation;
0.542 kg light gas oil, from
distillation; 0.711 kg residum,
0.260 643 0 1,070 5,237 199 -1,280 5,869
489