Process Modifications and Upgrades

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Reduction of energy consumption by modification of cement manufacturing process or upgrading the equipment to newer more efficient ones, will reduce the CO2 emissions either directly through reduction of fossil fuel requirements at the kiln, or indirectly through reduction of electrical demand. Energy efficiency methods are especially attractive because they can provide economic and environmental benefits.

8.4.1.1 Replacement of Kiln Capacity

In 2006, plants with wet and dry process kilns consumed, on average, 6.2 GJ/metric ton of cement (5.8 x 106 Btu/short ton of clinker) and 5.5 GJ/metric ton of cement (5.2 x 106 Btu/short ton of clinker) of fuel-based energy, respectively. In contrast, specific fuel consumption for the overall industry (including dry, wet, preheater and precalciner kilns) averaged 4.3 GJ/metric ton of cement (4.2 x 106 Btu/short ton of clinker), and plants with modern precalciner kilns consumed approximately 3.8 GJ per metric ton [24]. From these statistics, it is apparent that replacement of wet, dry, and older preheater kiln capacity with state-of-the-art precalciner kiln processes can yield substantial reductions in fuel use and commensurate reductions in CO2 emissions [25]. This observation is also supported by the data presented in Table 8.2 earlier.

Capacity replacements, such as those described above, have taken place continually over the history of the cement industry in response to increased market demand for cement. Generally, replacement of low-fuel-efficiency processes with higher-efficiency processes is done with an expansion in production capacity to take advantage of the economy-of-scale associated with capital costs.

8.4.1.2 Other Energy Efficiency Improvement Options

Opportunities exist within U.S. cement plants to improve energy efficiency while maintaining or enhancing productivity [23]. Energy efficiency improvements may be undertaken in various areas of a cement plant. Energy consuming equipment such as motors, pumps, and compressors require regular maintenance and replacement, when necessary. Consequently, a key component of plant energy management is ensuring efficient operation of crosscutting equipment that powers the production process of the plant. Another important component is ensuring efficient operation of the production process. In this regard, use of process optimization and the most efficient technologies is important.

Broadly, energy efficiency improvement options may be categorized under measures for raw materials preparation, measures for clinker making, measures for finish grinding, and plant-wide measures. Worrell and Galitsky [23] have examined these measures in some detail and have developed cost and performance estimates. Tables 8.3-8.6 list these measures and associated energy savings.

Table 8.3 Energy efficiency measures for raw materials preparation

Electricity consumption change (kWh/short ton clinker)

Table 8.3 Energy efficiency measures for raw materials preparation

Electricity consumption change (kWh/short ton clinker)

Energy efficiency improvement method

Dry

Wet

Preheater

Precalciner

Efficient transport system

-3.20

n/a

-3.20

-3.20

Raw materials blending

-2.70

n/a

-2.70

-2.70

Process control vertical mill

-0.90

n/a

-0.90

-0.90

High efficiency roller mill

-11.05

n/a

-11.05

-11.05

Slurry blending and homogenization

n/a

-0.35

n/a

n/a

Wash mills with closed circuit classifier

n/a

-12.00

n/a

n/a

High-efficiency classifiers

-5.05

-5.05

-5.05

-5.05

n/a=not applicable or data not available n/a=not applicable or data not available

Table 8.4 Energy efficiency measures for clinker making

Energy efficiency Electricity consumption change Heat input change improvement (kWh/short ton clinker) (106 Btu/short ton of clinker)

method Dry Wet Preheater Precalciner Dry Wet Preheater Precalciner n/a n/a n/a n/a n/a

Energy -190 -150 -190

Management and Control System (EMCS) Seal Replacement n/a n/a n/a (SR)

Combustion System n/a n/a n/a Improvement (CSI)

Indirect Firing (IF) n/a Shell Heat Loss Reduction (SHLR) Optimize Grate

Cooler (OGR) Convent to

Reciprocating Great Cooler (CGC) Heat Recovery for Power Generation (HRPG) Efficient Mill Drives (EMD)

-2.00 n/a n/a n/a n/a n/a=not applicable or data not available

Table 8.5 Energy efficiency measures for finish grinding

Electricity consumption change (kWh/short ton clinker)

Energy efficiency improvement method

Preheater Precalciner

Energy management and process control -1.60 -1.60 -1.60 -1.60

Improved grinding media [Ball mills] -1.80 -1.80 -1.80 -1.80

High-pressure roller press -16.00 -16.00 -16.00 -16.00

High-efficiency classifiers -3.85 -3.55 -3.85 -3.85

Table 8.6 Plant-wide energy efficiency measures

Energy efficiency improvement Electricity consumption change (kWh/short ton clinker)

Table 8.6 Plant-wide energy efficiency measures

Energy efficiency improvement Electricity consumption change (kWh/short ton clinker)

method

Dry

Wet

Preheater

Precalciner

Preventative Maintenance (PM)

-2.50

-2.50

-2.50

-2.50

High Efficiency Motors (HEM)

-2.50

-2.50

-2.50

-2.50

Adjustable Speed Drives (ASD)

-6.25

-6.00

-6.25

-6.25

Optimization of Compressed Air

-1.00

-2.50

-1.00

System (OCAS)

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