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Energy Audit in Steel Plant

• satyendra
• March 7, 2020
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• Energy, energy audit, Energy conservation, Energy consumption, Energy saving, fuel, heat, power, waste energy,

Energy Audit in Steel Plant

Iron and steel plants have a large number of processes which involves different cycles such as heating, cooling, melting, and solidification. These processes are highly energy intensive. There are also several forms of energies which are being used in these plants. Further, these plants not only have high specific consumption of energy, but the level of total energy requirement is also high since these plants have large production capacities. Also, share of the energy cost in the total cost of production is very substantial. Hence, the conservation of energy is of great importance for an iron and steel plant. There are several approaches which are being adopted for controlling the energy consumption.

In the recent years, big developments for reducing the energy consumption have taken place in the technologies and the processes employed in iron and steel plants. Now most of the processes are being operated near to their thermodynamic limits. Such an operation requires not only strict technological discipline but also a close monitoring of the processes, which in turn needs a well designed and a systematic energy management system.

Another important approach for controlling the energy consumption is through carrying out an energy audit. The energy audit is carried out for a department, process, unit, or system. It identifies the energy usage patterns, equipment efficiencies, and building efficiencies in order to determine and to propose energy efficiency measures. The result of a successful energy audit is (i) the decreased energy consumption, (ii) reduced raw material usage, and (iii) increased quality of the end product. Performing industrial energy audits makes it possible to save raw materials, energy, and to optimize the process.

There are many reasons for undertaking of an energy audit. These reasons can include (i) improvement of the energy performance and minimize the environmental impacts of the operations of the plant, (ii) identification of the behavioural change opportunities by evaluation of the current operations and maintenance practices, (iii) identification of the available technical opportunities by the evaluation of the performance and efficiency of the significant  energy-using departments, processes, units, or equipments/systems of the plant, (iv) identification of the opportunities available for re-use and recycling of the energy, (v) obtaining clear financial information regarding energy savings opportunities in order to  prioritize these items for the decision-making process, (vi) getting of a greater understanding of a part or all  of the energy usage patterns of the plant, (vii) identifying of the potential for using alternative energy supply sources, (viii) achieving of the compliance with the statutory requirements, (ix) complying with the objectives of the corporate social responsibility, (x) meeting of the stake holder expectations, (xi) assessing of a strategic plan aimed at minimizing the carbon footprint, and (xii) to contribute to the process for certification to  a formal energy management system.

The objectives of an energy audit can vary from one plant to another. However, an energy audit is usually conducted to understand how energy is used within the plant and to find opportunities for improvement and energy saving. Sometimes, energy audit is also conducted to evaluate the effectiveness of an energy efficiency project or program.

With the energy audit the management gets a better picture of the energy consumption in the various departments, processes, units and equipments/systems of the plant. Energy audit also identifies opportunities for improvement which often delivers immediate cost savings. Energy audit also helps the management in ensuring the s compliance with statutory requirements of various processes of the plant.

Energy audit consists of developing an understanding of the specific energy-using patterns of a particular department, process, unit, or equipment/system. It does not specifically refer to energy-saving measures. It does, however, suggest that understanding how the particular department, process, unit, or equipment/system uses energy which leads to identifying ways to manage the energy consumption.

There is no single agreed-upon set of definitions for the various levels of energy audits. In fact, there are several relatively similar definitions of an energy audit. Two of the popular definitions are given here. As per the first definition, the energy audit is defined as ‘a systematic, documented verification process of objectively obtaining and evaluating energy audit evidence, in conformance with energy audit criteria and followed by communication of the results’. In the second definition, the energy audit is defined as ‘the verification, monitoring and analysis of the use of energy and submission of technical report containing recommendations for improving energy efficiency with cost-benefit analysis and an action plan to reduce energy consumption’.

Whatever may be the definition, energy audit consists of an inspection, survey and analysis of energy flows for identification of the energy savings opportunities. The purpose conducting of an energy audit is to reduce the amount of energy input into the department, process, unit, or equipment/system, without negatively affecting the output.

The energy audit is a systematic assessment of current energy-use practices, from point of purchase to point of end-use. Just as a financial audit examines expenditures of money, the energy audit identifies how energy is handled and consumed, namely (i) how and where energy enters the department, process, unit, or equipment/system, (ii) where it goes and how it is used, (iii) any variances between inputs and uses, and (iv) how it can be used more effectively or efficiently.

The first thing which is needed to be done during the energy audit is the study of the energy balance. This is because the energy balance brings out many features of the energy usage. Further, energy audit requires considerations of all the energy related aspects during the audit. Some of the important aspects include (i) all types of energies such as fuel, heat, power, and utilities etc., (ii) critical temperatures, (iii) quality of energy, (iv) the status of the technology, (v) energy efficiency, (vi) specific consumptions, (vii) recovery, recycling and use of waste energy, (viii) energy going to environment and getting wasted, (ix) physical condition of the of the equipment and furnaces, (x) energy leakages, (xi) systems available for monitoring of the energy consumption, (xii) maintenance of systematic energy records, (xiii) energy related knowledge and experience of the personnel, (xiv) level of energy discipline available, and (xv) energy management system and controls available. Consideration of utilities (such as steam, compressed air, oxygen, and nitrogen etc.) is essential, since utilities require a large amount of energy during their generation. Also, the specific consumptions are required to be benchmarked with the consumptions being achieved in similar other plants.

Energy audits have various degrees of complexity and can vary widely. However, every energy audit typically involves (i) data collection and review, (ii) surveys and system measurements, (iii) observation and review of operating practices, and (iv) data analysis.

Energy audits performed externally tend to focus on energy-saving technologies and capital improvements. Audits conducted in-house tend to reveal energy-saving opportunities which are less capital intensive and focus more on operations. Steel plants which regularly conduct internal energy audits gain considerable experience in how to manage their energy consumption and costs. By going through the auditing process, employees come to regard energy as a manageable expense, are able to analyze critically the way the department, process, unit, or system uses energy, and are more aware of how their day-to-day actions affect the energy consumption.

Energy audit results into important benefits at three distinct levels. These benefits are (i) financial benefits which contribute to a reduction in operating costs, (ii) operational benefits which assist the management to improve the safety and productivity, and (iii) environmental benefits which concern mainly the reduction of carbon di-oxide (CO2) or other greenhouse gases (GHG) emissions. Each of these benefits is likely to be realized progressively and to have a cumulative effect. The principal benefits can become available immediately from no-cost measures, or can involve some period before a return on investment is achieved. Others can only be realized when long-term plans are implemented.

Energy systems follow laws of thermodynamics. Hence, the energy auditing applies a simple natural law which is the first law of thermodynamics, also known as the law of conservation of energy. It simply means that the energy is to be accounted because it is neither created nor destroyed in the department, process, unit and equipment/system where it is used. Translated into practical terms, this law means ‘energy which comes in = energy which goes out’. The challenge of an energy audit is to define the system being considered and to measure energy flows into and out of the system.

The first of these challenges is to define the boundary of the department, process, unit, or equipment/system. The department, process, unit, or equipment/system can be the energy-consuming building, area within a building, an operating system, a collection of pieces of equipment, or an individual piece of equipment. Around these elements, a figurative boundary can be defined for the energy audit. The Fig 1 shows the schematic diagram of the chosen elements for defining the boundary for the energy audit.

Fig 1 Defining the boundary of the energy audit

The second challenge is more difficult technically because it involves collecting energy flow data from various sources through direct measurement. It is also likely to involve the estimating of energy flows which cannot be directly measured, such as heat loss through a wall or in vented air. Keeping in mind that the only energy flows of concern are those which cross the system boundary, the issues which are needed to be considered when measuring energy flows include (i) to select convenient units of measurement which can be converted to one unit for consolidation of data (e.g. to express all measurements in equivalent kWh, kcal or MJ), (ii) to know how to calculate the energy contained in material flows such as hot water to drain, cooled air to vent, intrinsic energy in processed materials etc. and (iii) to know how to calculate heat from various precursor energy forms, such as electricity converted to heat through the operation of an electric motor.

For the energy audit, sometimes the terms ‘macro-audit’ (also known as preliminary audit, or walk through audit) and ‘micro-audit’ (also known as detailed audit or diagnostic audit) are used. These terms refer to the level of details of an audit. Level of details is the first significant characteristic of an audit. The second significant characteristic is the physical extent or scope of the audit. The scope of the energy audit means the defining of the audit boundary in terms of the number of departments along with their processes, units, and equipments/systems.

The macro-audit generally starts at a relatively high level in the structure of energy-consuming departments, processes, units, and equipments/systems, perhaps the entire plant, and addresses a particular level of information, or ‘macro-detail’, which allows energy management opportunities to be identified. A macro-audit involves a broad physical scope and lesser detail.

The micro-audit, which has a narrower scope, frequently begins where the macro-audit ends and works through analysis to measure levels of greater detail. A micro-audit can be conducted for a process, a production unit, an energy-consuming system, or for an individual piece of equipment. Generally, as the level of the detail an audit increases, its physical scope decreases. The opposite is also true that is if the scope is increased, the level of detail of the analysis tends to drop. Generally, the internal energy audits are carried out as macro-audits than as micro-audits. Micro-level analysis requires expertise in engineering and analysis.

The procedure for conducting the energy audit is similar to the conducting of any other audits such as technical audit, environmental audit, or quality audit etc. In conducting the energy audit, there are also three main steps which are (i) planning and preparation, (ii) execution which includes collection of data, its analysis and evaluation, and (iii) documentation and reporting. Each of these three main steps has several sub-steps. These sub-steps are dependent on the nature of the audit and the objective of the audit. Steps in the process of energy audit are shown in Fig 2.

Fig 2 Steps in the process of energy audit

The assessment findings of an energy audit are only as good as the knowledge and experience of the auditor who performs the audits and assessments. Auditor is to be technically competent and sound.  He is to be even tempered, is required to possess integrity, remain objective, and report only what is observed. He is to maintain proper confidentiality of the findings.  He is required to have good information gathering and communication skills. His capabilities are to include the demonstrated ability to extract and provide information, analyze that information, and report the results accurately. He is to be qualified to perform the audit duties by virtue of education, training, and/or experience.  He is required to know the audit techniques, is to be competent in the subject under assessment, and is to be familiar with basic energy concepts and principles.   The key is that the auditor is to possess the needed audit expertise and subject matter knowledge for the scope of the audit. There are normally three general requirements for the auditors as given below.

• The auditor is to have the adequate professional proficiency for the audit. He is required to have the technical knowledge and auditing skills necessary for the audit.
• The auditor is to be free from personal and external barriers to independence, organizationally independent, and able to maintain an independent attitude and appearance. He is to maintain independence so that audit findings are both objective and viewed as objective by knowledgeable third parties.  The auditor is to consider not only whether he is independent and whether his attitudes and beliefs permit them to be independent but also whether there is anything about his actions in some situations which might lead others to question his independence.  All situations deserve consideration because it is essential not only that the auditor is to be independent and objective in fact but also the knowledgeable third parties consider him to be so as well.
• The auditor is to use due professional care in conducting the audit and in preparing related reports. It is the auditor’s responsibility to follow all applicable standards in conducting audits.  Auditor is to use sound professional judgment in determining the standards which are to be applied to the audit.  Exercising due professional care includes use of sound judgment in establishing the scope, selecting the methodology, and choosing the tests and procedures for the audit.  The same sound judgment is to be applied in conducting the audit and in reporting the findings.

During the energy audit, the following seven attributes of the data or the information are to be maintained and ensured.

• Effectiveness – It deals with the information being relevant and pertinent to the audit objectives as well as being delivered in a timely, correct, consistent and usable manner.
• Efficiency – It concerns the provision of information through the optimal (most productive and economical) usage of resources.
• Confidentiality – It concerns with the protection of the sensitive information from the unauthorized disclosure.
• Integrity – It relates to the accuracy and completeness of information as well as to its validity in accordance with the organization’s set of values and expectations.
• Availability – It relates to the information being available when needed for carrying out the audit, and hence also concerns the safeguarding of the resources.
• Compliance – It deals with complying with the laws, regulations and contractual arrangements for meeting of the audit objectives i.e., externally imposed criteria for the data and the information. This essentially means that audit is to be conducted within the ambit of rules, regulations and/or conditions of the organization.
• Reliability of the information – This means the data and information used for the audit is to be reliable.

The problems or failures associated with the energy audit are due to the lack of audit preparation, checklist, or audit criteria elements, auditor skills and knowledge, commitment from the management, and bureaucratic reporting. The audit checklist is for the reference of the auditor and helps the auditor to conduct the audit work in a systematic and consistent way. Systematic approach to the auditing is the first element for successful energy audit. The systematic audit program includes initiating the audit, preparing for onsite audit, conducting on site audit, report preparation and submission.