ENERGY BENCHMARKING AND CARBON FOOTPRINT REDUCTION OPPORTUNITIES IN PORTLAND CEMENT MANUFACTURING PROCESSES IN NIGERIA

ABSTRACT

Energy benchmarking and carbon footprint reduction opportunities in Portland cement manufacturing processes in Nigeria are presented. Life Cycle  Assessment (LCA) is used to estimate the environmental impact of three cement manufacturing processes in Nigeria. The energy consumption of the cement manufacturing processes are evaluated using energy Benchmarking  and Energy  Savings Tool for cement (BEST-Cement). BEST-Cement  evaluates  and  compares  the  energy  consumption  of  the  cement manufacturing processes in Nigeria to China (world largest producer of cement) and International  energy   benchmark  practices.  Energy  Conservation   Supply  Curves (ECSC) were used to evaluate energy and emission reduction mitigations measures through the application of energy efficient measures/technological changes. A list of 34 energy   efficiency  measures/technologies   were  applied  as  per  the  technological requirement  of each cement  manufacturing  process  technology  in constructing  an Energy  Conservation  Supply  Curve  (ECSC).  The  carbon  footprint  of  1  tonne  of Portland  cement  produced  by  the  wet,  semi-wet  and  dry  cement  manufacturing processes in Nigeria estimated using the 100 years Global Warming Potential (GWP) value are 871 kg of CO2 Eq, 694.45 kg CO2 Eq and 621 kg of CO2 Eq respectively per tonne. The average technical potential for thermal and electrical energy savings for the three  cement  manufacturing   processes   when   compared  to  International  cement manufacturing energy benchmarks were 35% and 39.27%. When compared to Chinese cement manufacturing energy benchmarks, the average technical potential for thermal and electrical energy  savings were 29% and 25.56% respectively. Results from the Energy  Conservation  Supply Curve model, indicates that the cost-effective  energy efficiency  potential  for  the  wet cement  plant  in  2010  is 235,038  GJ/year,  which accounts for 6.87% of primary energy,  for the semi-wet process it is  estimated at 237,913GJ/year which accounts for 8.89% of primary energy and the dry cement plant VII estimated  to be 374,055GJ/year  which  accounts  for 14%  of primary  energy.  The reduction  in  carbon  footprint  emissions  due  to  use  of  selected  energy  efficiency measures/technological changes applied to the Conservation Supply Curves estimates that a total of 12,362 tCO2Eq per year, 12,694 tCO2Eq per year and 20,502 tCO2Eq per year are achieved for the wet, semi-wet and dry cement manufacturing processes in Nigeria respectively.

CHAPTER ONE

 INTRODUCTION

1.1       Introduction

Climate change is increasingly being recognized as a major global challenge, and many organizations and individuals are actively trying to quantify their impact and also reduce Greenhouse Gas (GHG) emissions due to their activities (Doyle, 2009). It is widely accepted that products and services that human beings utilize indirectly or directly generate GHG emissions. The GHG emissions from anthropogenic sources are on the rise and thus warming up the planet causing adverse change in weather conditions and patterns around the world (GHG Schemes Addressing Climate Change, 2011). The extensive use of fossil energy resources in world manufacturing industry contribute significant amount of GHG emissions to the environment (World Energy Resources, 2013).

One of such manufacturing process that contributes to the generation of GHG emission is cement manufacturing. Cement manufacture is a major mineral commodity industry and cement production process is a highly energy intensive process (Ohunakin et al, 2012). The energy consumed by world cement industry is estimated at about 2% of the global primary energy consumption, which is equal to 5% of the total world industrial energy consumption (Worrell et al, 2001). The world cement industrial sector is believed to emit about 5% – 7% of the world total CO2 anthropogenic emissions (Schneider et al, 2011).

1.2 Cement

The British Standard (EN 197-1:2000, 2004) for cement defines cement as a hydraulic binder, i.e. a finely ground inorganic material which, when mixed with water, forms a paste which sets and hardens by means of hydration reactions and processes and

which, after hardening, retains its strength and stability even under water. Cement is mostly grey in colour and it is used majorly as a bonding agent in production of concrete: concrete is a mixture of inert mineral aggregates, e.g., sand, gravel, crushed stones, and cement. It is used majorly for civil construction. Portland cement is the most popularly and commonly cement in use in the world (Bell, 2007).

Generally there are two types of Portland cement, they are the Ordinary Portland Cement (OPC) and the Blended Cement (BC), which is available as slag or Portland Pozzolana cement. (PPC). The Ordinary Portland cement contains mixture of clinker and gypsum ground to a very fine powder while the BC is manufactured by blending a mixture of Ordinary Portland cement with Pozzolana materials (Fly Ash) to form PPC or with slag. The mixing proportions of OPC and the Pozzolana materials or slag is not less than 15% and not more than 35% by weight of cement (Pofale and Wanjari, 2014).

1.2.1 Cement Standards

Cement standards vary considerably with regional and climate conditions across the globe, this is due to the type of raw materials available, economic and industrial development of a nation .This has led to significant variations in composition and national standards of cement made in different countries. There are two major standards, they are the C150 of American Society for Testing and Materials (ASTM) and BS EN197-1:2000 of the British Standards Institution (BSI) standards (Yahaya, 2009). The BS EN 197-

1:2000 describes 27 types of cement which are divided into 5 groups, as shown in Table

1.1

Table 1.1 Cement Types

	Types of Cement	Clinker %	Other Constituents
CEM I	Portland	95 – 100
CEM II	Portland – slag	65 – 94	Blast furnace slag
	Portland – silica	90 – 94	Silica fumes
	Portland – Pozzolana	65 – 94	Pozzolana
	Portland – fly ash	65 – 94	Fly ash
	Portland – burnt shale	65 – 94	Burnt Shale
	Portland – limestone	65 – 94	Limestone
	Portland – composite	65 – 94	Additives mix
CEM III	Blast – furnace	5 – 64	Additives mix
CEM IV	Pozzolanic	45 – 89	Additives mix
CEM V	Composite	20 – 64	Additives mix

British Standard EN 197-1:2000, (2004).

Nigeria cement industry majorly produces Ordinary Portland Cement (OPC) and they are regulated by the Standards Organization of Nigeria (SON) (Clean Development Mechanism, 2006). SON grades Ordinary Portland cement types available in the country under a new regulatory regime which is tagged “NIS 444-1” summarized in the Table 2.2

Table 1.2 The Standard Organization (SON) Portland cement grading “NIS 444-1”

No:	TYPE	USE/APPLICATION	REMARKS
1	CEM  I  &  II	This  grade  is  only  to  be  used  for   finishing works in a building such as plastering.	This   grade   is   also
	32.5R		called 32.5N or 32.5. It is also the lowest grade
2	CEM  II	This  grade  will  be  used  for  molding   blocks   and   casting   works   such   as columns, beams and slabs	This   grade   is   also
	42.5R		called 42.5N or 42.5
3	CEM I 52.5R	This  grade  will  be  used  for  bridge   construction.	This   grade   is   also   called 52.5N or 52.5

Franca (2014)

These grading numbers indicates the minimum compressive strength gained by the cement-sand mortar mix in 28 days. 32.5 Grade signifies that 28 days strength of the cement will not be less than 32.5 N/mm2 and similarly for other grades as well (Rao et al.,

2010).

1.2.2 Cement manufacturing in Nigeria.

In Nigeria, the cement manufacturing sector has been steadily growing coupled with the aggressive privatization embarked upon by the Federal Government of Nigeria. Data obtained from the Cement Manufacturers Association of Nigeria (CMAN) shows cement plants in Nigeria in Table 2.3 as at 2009.

Table 1.3 Cement plant locations, capacities and cost of installation

Company Name	Location	Production   Capacity(tonnes)	Cost of   installation/Expansion(USD)
Lafarge WAPCO	Ewekoro	2,000,000	130,000,000
Lafarge WAPCO	Shagamu	1,000,000	NA
Lafage WAPCO	Lakatabu	2,000,000	600,000,0000
Dangote Cement Grp	Ibese	6,000,000	1,020,000,000
Dangote Cement Grp	Obajana	6,000,000	1,200,000,000
Dangote Cement Grp	Obajana	5,000,000	1,000,000,000
AVA Cement	Edo	300,000	NA
Benne Cement	Benue	3,000,000	400,000,000
Dangote Cement Grp	Benue	1,000,000	200,000,000
Unicem	Calabar	2,500,000	840,000,000
Ashaka Cement	Gombe	1,000,000	150,000,000

Source: Bafuwa, 2011. NA = Not available.

In 2014, Nigeria became the largest cement producer and consumer of cement in the Sub-Saharan Africa region, with an estimated production capacity and consumption rate per annum of 28.3 million MT and 18 million MT respectively (Aithnard, 2014).

Dangote Cement Plc an indigenous company is the largest producer of cement in Africa with cement plants spread across the continent, followed by Lafarge Cement Plc in production capacity. Based on a report by Renaissance Capital (Sterling, 2013), a leading investment bank in Nigeria, Nigeria is set to maintain this position as investors invest over the  medium term.  With the  current trend  of  investment it  is  predicted that  cement production capacity in the country will peak in 2020 at just under 50 million tonnes per annum.

1.2.3 Cement manufacturing processes and technologies

Cement production processes were developed to achieve complete burning of cement raw materials majorly limestone (CaCO3) in a process called calcination (Worrell and Galitsky, 2004). Calcination is the process of decarbonising and sintering of limestone and other additives (shale, iron ore e.t.c) at a very high temperature usually around 1400 o C to produce clinker. Clinker is the major material used in production of cement.  The calcination and sintering of limestone and other additive takes place in a kiln system and the calcination process is a huge source of GHG emission in cement production process (Huntzinger and Eatmon, 2009).

Different manufacturing technologies have been developed to achieve complete burning of limestone and other addictive, with the aim of reducing energy consumption and GHG emissions from the process. They are categorised as the wet cement manufacturing process, semi-wet/semi-dry cement manufacturing process and dry cement manufacturing process (Nisbet and VanGeem, 1997). Three of the cement manufacturing processes mentioned above are available and in full operation in Nigeria.

The differences that set the wet, semi-wet and dry cement production process apart, can be observed in cement raw material preparation method prior to calcination in the kiln. In the wet process, 27% to 38% w/w of water is added to clinker raw materials to form thick slurry and same in the semi-wet process 11% to 17% w/w of water is added to clinker raw material. The water addition is in percentage of the dry raw materials used. The dry process is based on the preparation of a fine powdered clinker raw materials through grinding, after which the raw material is dried using the exhaust of the Kiln system. The choice of the process is mainly based on the chemical homogeneity of the available raw materials (Worrell and Galitsky, 2004).

With the cement market still expanding, increase in cement production in Nigeria will invariably lead to increased energy consumption and more GHG emissions from Nigeria’s cement industry. As such, there is a need to measure, estimate, and establish current level of energy consumption and GHG emission from cement manufacturing process utilized in Nigeria. The level of energy consumption and the amount of GHG emissions from cement manufacturing processes in Nigeria, can be established through energy benchmarking and carbon footprint estimation.

Energy utilization efficiency is a major determinant of the profitability of manufacturing system (Fadare et al., 2010). Energy benchmarking serves as valuable tool for improving our understanding of energy consumption pattern of manufacturing process and helps in  setting acceptable bases for comparing local energy consumption of a particular product or system to internationally established best practices (Ruth et al., 2001). GHG emission associated with the type of energy utilized by the cement manufacturing process can be estimated by establishing the carbon footprint of cement.

Carbon footprint evaluation is an effective means of measuring the Carbon Dioxide (CO2) and other GHG impact of a  product, process or organization on  the climate (Weidmann, 2009). According to Wu (2011), it as an indicator of climate performance, helping to identify major GHG emission sources and potential areas of improvement. When they are calculated for products, they are called product carbon footprints. The evaluation of the product, processes or organizational carbon footprints help government and environmental NGOs to set acceptable safety limits by which cement factories should operate. It also give the collective citizenry an opportunity to  know the carbon content of products they consume and therefore take collective decision on production, utilization and eventual disposal of such product.

The energy and carbon footprint reduction opportunities in cement manufacturing processes can be explored through the construction of Conservation Supply Curves (CSCs). Conservation Supply Curves (CSCs) were developed to describe and compare the different options for energy conservation in a transparent way (Fleiter et al.,

2009). CSC is a tool for investigating the technical potential and economics of the energy conservation measures. The use  of  Conservation Supply Curves in  selecting energy efficiency measures and technological changes to apply in reducing energy consumption in cement industries across the globe are well studied (Hasanbeigi et al., 2013). Thirty four energy  efficiency measures/technologies are  identified  and  used  in  constructing  the Conservation Supply Curves. The quantity of GHG emissions reduced and the cost of implementing such energy efficiency measures/technologies is reported in the study.

This work will study the energy consumption pattern of the cement manufacturing processes and carbon footprint of cement manufacturing processes in Nigeria.

1.5 The objectives are to:

1)  Benchmark energy consumed in the production of 1 tonne of Portland cement by the wet, semi-wet and dry cement manufacturing process in Nigeria and compare energy  consumption  with  cement  manufacturing energy  benchmark  practices reported in China and the World.

2)  Generate carbon footprint process map and identify the process with highest carbon footprint, thus the highest technical potential for improvement.

3) Apply the concept conservation supply curve in selecting carbon footprint mitigating energy efficiency measures / technologies that cut across the three manufacturing process under study.

4)  Estimate the average GHG emission from the three cement manufacturing process in Nigeria.

1.6      Significance of study

This study evaluates the carbon footprint of Portland cement produced in Nigeria by conducting a Life Cycle Assessment (LCA) of cement manufacturing processes, making use of data from comprehensive cement production report from the wet, semi wet and dry cement manufacturing processes under the operation of Lafarge Cement Plc in Nigeria.

As emissions from our cement plants increase due to production increase or system inefficiencies, there is a need to quantify and compare current performances in order to determine if our production systems are functioning optimally. Calculating organisational

or product energy use and carbon footprint is one way of establishing performance, and the first step towards improvement.

This study provides a simplified eight step carbon footprint reporting and accounting standard adapted from the Greenhouse Gases Product Accounting and Reporting Standard, of World Resource Institute (WRI) and World Business Council for Sustainable Development (WBCSD). The study also benchmarks the energy consumed in each  of  cement processing step.  Completing an  energy benchmark exercise helps a company or organization understand where they are as a company or organization on their energy consumption level, where they want to be and help establish major deliverables and milestones that will help reduce energy consumption level to compete favourable.

1.7 Scope of study

This study will consider wet, semi-wet and dry cement processes for cement manufacturing in Nigeria. The following cement processing steps are identified; Quarry and Crushing process step, raw meal (grinding and homogenization) process step, pyro- processing process step and cement finish grinding process step. They are analyzed under the wet, dry and semi-wet cement manufacturing process.

The current energy consumption by the three cement manufacturing processes will be benchmarked and compared against the energy benchmarks of world largest producer of Cement “China” and World energy benchmarks for cement manufacturing processes. The Energy Benchmarking and Energy Savings Tool (BEST) for cement is a process based tool developed by the Lawrence Berkeley National Laboratories used to benchmark current technology performance (Hasanbeigi et al., 2012).

The carbon footprint emitted per tonne of Portland cement produced from the three cement manufacturing process mentioned are established for current cement manufacturing technologies. The  carbon  footprint  of  cement  produced  by  processes mentioned above are carried out by bottom-up process analysis method of estimation. The GHG Protocol for Product Accounting and Reporting Standard and the Publicly Available Specification (PAS) 2050 created by the British Standard Institute (BSI) and co-sponsored by Carbon Trust, are standards adhered to in establishing the carbon footprint of cement.

The Conservation Supply Curve (CSC) is used in selecting energy efficiency measures/technologies which would be applied across cement production processing steps of manufacturing processes enumerated above. A Microsoft Excel Spreadsheet is used in conducting Life  Cycle  Assessment analysis and  computations. Energy and  emission conversion factors were obtained from the National Renewable Energy Laboratory’s US Life Cycle Inventory Database (NREL) and are applied in conducting life cycle assessment of cement manufactured by the afore mentioned processes.

1.8 Limitation of studies.

There are five processing steps identified in the manufacturing of cement. The cement packaging process step is not included in the study. The scope 3 emissions are not estimated in the work, the cost of electricity, cost of fuel and cost of carbon reduction technologies utilized are reported in Naira. The fuel used in both wet and dry cement manufacturing process in the pyro-processing process step is natural gas and the fuel used in the semi-wet pyro-processing process step is fuel oil. The base year of analysis for the study is 2010.

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