7 Secrets to Sustainable Material Usage Reduction

Tight process control

is essential for sustainable

material usage reduction

“Materials” in the industrial context could refer to the raw materials used to manufacture a product, materials in various stages of transformation throughout the manufacturing process or finished product. In all cases materials could be lost, and the objective of material usage reduction is to reduce the quantum of these losses. Reducing the amount of materials used in manufacturing is one of the most powerful cost-reduction strategies manufacturing organisations can take. When the life cycle impacts of materials are considered, it is also most likely the highest-leverage approach for the reduction of environmental footprint. Yet, in downturns such as what we are experiencing now, many manufacturing organisations still turn to reducing staff numbers as the primary approach to maintaining profitability, an approach which for social reasons and also in terms of unintended consequences is unsustainable.

How then does an industrial organisation best tackle material usage reduction and maintain high levels of performance in this area in the long term?  The following are general guidelines based on my experiences with organisations that are able to sustainably reduce material usage:

1.        Invest in Material Usage-specific Process and Equipment Knowledge

It is vital that those accountable for material usage have a deep understanding of the manufacturing processes they control, not just in terms of how to operate them to produce product, but also in terms of the drivers of material usage within these processes. Losses can arise from issues concerning individual pieces of equipment, but also from how individual processes interact with each other. These linkages need to be well understood in order to control material usage consistently.

2.       Tighten up Material Accounting Systems

Managers require believable material usage data in order to make informed decisions regarding the maximisation of material yields. While the design of accounting systems is typically fairly straightforward, accurate recordkeeping is often a problem. It is important that stocktaking procedures are rigorous for raw materials, work in progress and finished product. Records of receipts and dispatches should also be accurate and apply to the period being reviewed. Wherever possible, material usage reports should be produced daily, minimising the time required to detect and act on usage problems. Finally, every instrument used for measurement should be accurate and well maintained.

3.       Implement Short-interval Control Systems at Source

Plant operators and supervisory staff have accountability for material usage, and therefore require the systems to measure and manage it. The systems employed here should indicate what usage levels are at any point in time, but should capture additional process-specific information which would allow shop floor staff to gain important insights into the reasons for deviations to usage standards. Hence the yield information for a reduction furnace should be displayed side by side with the mass of process chemicals added, the furnace temperature, the precise time that the furnace was charged and when it was tapped, flue gas temperatures and any other information deemed relevant to material usage.

It is important here that where an important piece of information is not routinely measured but is relevant to material usage, that such information becomes part of routine. Hence in our example outlined here, it may be worthwhile to measure the amount of valuable metal contained in slag removed from the furnace for a few selected batches each week. Such decisions depend on the costs of additional tests relative to the potential savings to be made from access to the information.

It is also useful to automate short-interval control systems as far as possible to allow operators to focus on control of the process rather than become bogged down with administrative duties.

4.       Involve the Maintenance Function

If plant maintenance is viewed as something that is required for the sake of plant uptime only, a massive opportunity is lost in terms of the contribution of good plant maintenance to material usage reduction. Functional failures can occur which do not stop a manufacturing facility from running, but which have serious consequences for material usage.

It is important that in the development of a maintenance programme for a manufacturing plant, the material usage impacts of failures are fully appreciated and factored into the risk assessment for individual failures. Preventive maintenance tasks are generally designed to be proportional in effort to the consequences of failure, and hence these types of failures will be accorded the correct amount of resources in assuring their prevention should the maintenance function be fully engaged in the reduction of material usage.

A further benefit of involving the maintenance function is that failures which result in losses of materials will receive a greater level of urgency in terms of their correction once they have been detected. In high-volume manufacturing, cost deviations multiply rapidly and speedy correction of problems is crucial.

5.       Keep Track of Waste Generated

Material usage is always accompanied by liquid and/or solid and/or gaseous waste streams, and the extent and characteristics of these waste streams relate to the extent of the material losses. It is therefore important that these streams are closely monitored, since they can provide more important clues as to the reasons for excessive material usage. In the electroplating industry, for example, the volume of effluents and the concentrations of individual metal ions in these effluents point operators to the magnitude of the drag-out losses being experienced in the plating operation.   

6.       Integrate Quality and Cost Management

Rework always comes at a cost, even at facilities which have the capabilities to recycle defective products in order to recover raw materials. In many instances, poor quality product cannot be reworked and has to be destroyed - a worst-case scenario in terms of material losses. A powerful cost reduction strategy is therefore to focus resolutely on quality, not just in terms of final product, but for every individual process step employed.

Question what you do continuously, and understand the measures taken in the name of material usage reduction which may be negative for product quality and vice versa. There is an optimum point at which you should be operating which maximises quality while minimising material usage.

7.       Assess Raw Material Performance

The raw materials used in manufacturing are typically purchased according to defined specifications, but variations within these specifications can sometimes have an impact on how the materials behave from a yield perspective. In some industries not even comprehensive specifications can adequately account for the characteristics of materials and how they will behave when processed. Materials can also exhibit changes in characteristics during storage.  It is therefore not sufficient to simply procure to a specification – one has to closely monitor the performance of each batch of material used to assess whether there are any negative material usage impacts arising from its use. This is particularly important when there has been a change in supplier or changes in the processes employed by existing suppliers.  Action can then be taken to resolve the problem at source.

The above are some of the more easily-identifiable operating practices which I have observed to have a positive impact on material usage. Each one requires significant effort to implement. When we assess the impact that material usage has on the financial and environmental performance of a manufacturing unit however, I am sure you will agree that the potential rewards are worth the effort.



Reducing Peak Demand Charges at Industrial Sites

Short-term electricity costs are expected to continue to increase globally due to the costs associated with investments in renewables as well as increases in the prices of commodities such as coal, oil and gas (with some exceptions in the short term regarding shale gas resources). In South Africa, price increases are driven by these issues along with a massive investment programme by the national power utility, Eskom, which includes coal-fired and nuclear options as well as some peaking capacity. Electricity users in South Africa have experienced a doubling in electricity prices over the last 3 years. Indications are that double-digit increases will continue, albeit at a somewhat reduced level. The implications are that any previously considered investments regarding power savings should be regularly reviewed by users, since their viability will continue to improve.

Given this context, energy-intensive industrial organisations around the world cannot afford to be without a meaningful plan to reduce electricity costs. This post will address what can be done to reduce peak demand charges, typically a significant cost for industrial operations.

Electricity bills typically comprise a number of different elements, with the two major ones being charges for the quantity of energy consumed in the billing period (measured in kWh) and charges for peak demand (measured in kVA). Tariff structures can vary widely, depending on user size, location and other determinants. For energy consumption, either a flat rate is applied or users could be billed according to “time-of-use” charges, which vary the rate based on the time of day during which the energy is consumed and/or the time of year. Variable rate schemes are designed to change behaviour such that the installed power generation base can be optimally employed and maintained. 

In the case of peak demand (also called "maximum demand") charges, a flat or variable rate is typically charged for each unit of apparent power consumed, based on the highest apparent power demanded in the billing period. Demand is monitored over defined intervals (for example time buckets of 15 minutes) to arrive at the peak demand level for which a site is billed. This billing strategy is generally applied during periods of peak electricity consumption. Hence weekends could be omitted, as could periods from 10p.m. until 6a.m. during weekdays. You will need to review your own tariff scheme and respond to that when trying to reduce your bills.

The 3 basic strategies that electricity users can employ to reduce peak demand charges are load shifting, power factor correction and the implementation of energy efficiency measures.

Load shifting

Electricity users can schedule high-demand processes such that they do not operate together, thereby reducing the overall peak for the site. Some processes may also be operated during periods in which peak demand charges do not apply. In planning such a strategy, one has to be mindful of the costs involved. For example, there may be overtime costs payable if plant operators are required to work outside of normal working hours in order to operate part of the plant. Of course, the needs of your customers will also drive the applicability of this approach, since it may conflict with your goals regarding the reliable supply of product.

This strategy, while it does have some application in industry, is difficult to apply in large continuous operations and is more suitable to batch-type operations or operations where short continuous runs are possible. For example, a site may have a number of production lines, all of which may not need to run at the same time. It is generally also true that where individual lines have significant excess capacity, the strategy is more easily executed. It is very useful to have a flexible labour force with plant operators who are capable of operating different production units when trying to implement load shifting, since this helps to prevent a situation developing where workers are idle.

Use of Power factor Correction

Power factor correction is a widely-accepted technological approach used to reduce peak demand. In order to explore this further, we need to review some basic theory regarding power and typical AC circuits. In AC circuits, voltage and current follow sinusoidal patterns. When voltage and current waveforms peak and trough at exactly the same point the waveforms are said to be “in phase”. Inductive and capacitive loads in a circuit can however cause these waveforms to become “out of phase”, with inductance causing the voltage to lead the current and capacitance causing the current to lead the voltage. The angle by which these waveforms are out of phase is known as the phase angle (ф). Power factor correction tries to get voltage and current back into phase in circuits which have an inductive nature by introducing additional capacitance.

Inductive loads such as motors, electromagnetic ballasts in light fittings, induction furnaces, transformers and the like are common on industrial sites, and tend to increases the amount of apparent power required. The bigger the difference between the apparent power (measured in kVA) and the real power (measured in kW) consumed, the lower a site’s power factor (Power factor = kW/kVA) at any instant in time and the higher the peak demand charges the site would have to pay. Note that what is important here is the power factor at peak demand, since a low power factor at low demand levels will not have an impact on demand charges. If the amount of apparent power can be reduced, peak demand can be reduced without any change in real power consumed. 

Apparent power is the vector sum of real power (in kW) and reactive power (in kVAr).  

Power factor = Real power / Apparent power =  kW/kVA = cosф.

When kW = kVA, power factor = 1, ф = 0 and hence kVAr = 0. In order to improve power factor, a quantity of capacitance that will reduce the reactive power to a level corresponding to the desired power factor is required.  Capacitance and inductance offset each other directly.

Example:

A site has a measured power factor of 0.8 at a peak demand level of 700 kVA. Calculate the amount of capacitance required to achieve a power factor of 0.98.

Since PF = 0.8, the real power consumed = 0.8 x 700 = 560 kW

Apparent power²  = Real power² + Reactive power²

Reactive power     = Square Root (Apparent Power² – Real  Power²)

                             = Square Root (700² – 560²)

                             = 420 kVAr at a power factor of 0.8

At a power factor of 0.98, the Apparent power “consumed” = 560 / 0.98 = 571.4 kVA

Reactive power  = Square Root (571.4² – 560²)

                          = 113.7 kVAr at a power factor of 0.98

The net capacitance required to correct the power factor is therefore 420 kVAr – 113.7 kVAr = 306.3 kVAr. 

Capacitors are typically arranged in banks downstream of the transformers through which power is delivered to the site, and are accompanied by devices such as harmonic filters and controllers which control the amount of capacitance applied.

Energy Efficiency

Improvements in energy efficiency can have a significant impact on peak demand, but the relationship between the two depends on the specifics of the efficiency intervention concerned. Energy efficiency implies a reduction in the quantity of real power consumed. It is however possible to reduce the amount of energy consumed by a process without impacting on peak demand. The point here is that peak demand is based on the maximum apparent power drawn over a limited period of time rather than the total amount of energy consumed. 

Consider a heating element, for example. It may have a specific power rating, say 100 kW.  When on, it will consume this quantity of power, and if it is on at the same time as other large loads, the peak demand for the site concerned may not change. The element may however be used for shorter periods (due to insulation of the equipment in which it is installed for example), reducing total energy consumption i.e. the total kWh consumed by the element will be lower, but not the kW consumed. For resistive components such as heating elements, apparent and real power are equal. 

On the other hand, installation of a high-efficiency motor with a similar power factor to the standard-efficiency motor it has replaced will both reduce energy consumption and maximum demand (assuming the motor runs continuously, or during periods of peak demand).  

In general my approach is to look at energy efficiency and reductions in peak demand separately, with any demand benefits accruing due to energy efficiency projects considered to be a bonus. An exception is where opportunities exist to fundamentally change a process through, for example, the elimination of unnecessary energy-intensive unit operations with large inductive loads.  

THE BASICS OF INDUSTRIAL WATER MANAGEMENT STRATEGY

Business strategy is about making choices which will support growth. Resource management strategies should be aligned to business strategy, and are about ensuring that organisations have a ready supply of resources to enable growth, use these resources as efficiently as possible and have as little impact on the environment as possible in the use of these resources.

Water is widely used in industry and even organisations that appear to use very little water per unit of production can have an enormous impact on water resources. In order to determine whether your organisation requires a water management strategy as part of its broader sustainability strategy, it is important to review your water use from a number of perspectives.

Industries interface with water resources in a number of ways:

·         Many of the raw materials used in industry require water for their production and have the potential to incur pollution of water resources during their production;

·         In water-scarce environments, industries can have a real impact on the availability of water for downstream users, both in terms of quantity and quality. In a country such as South Africa, which has an extensive water transfer network, the impacts are often felt far away from the location in which the water is ultimately used;

·         Industry can have negative impacts on local ecosystems when the water required to remain in watercourses in order to sustain the local ecology (the so-called “reserve”) is not maintained;

·         Abstraction of water can impact on the aquatic environment through the entrainment and impingement of aquatic fauna and flora – the design of abstraction systems is important here, but for very large users, the sheer volume involved makes mitigation challenging;

·         The quality of incoming water dictates the impact it will have on processing operations (e.g. scaling of heat transfer surfaces) and the treatment options industries need to exercise before the water can be used – this is an example of how, while industries impact on water quality, incoming water quality also has a profound impact on industrial operations;

·         Industries ultimately integrate themselves into the macro water cycle, and the precise manner in which they use water dictates how they will impact on that cycle. If large quantities of water are evaporated, this water will not become available to downstream users, while if water is not evaporated but discharged, its quality determines its impact on downstream users. This in turn determines how these users will employ the water in their operations, and their impact on the water cycle. There is therefore a “systems effect” which industrial water users impose on other water users;

·         Water management issues can have significant impacts on issues which on the surface appear unrelated to water. For example, irrigation of pastures with treated effluent could introduce pollutants into the food chain;

·         Much is made of the so-called “water energy nexus”, but in industrial environments, water use impinges on energy, material usage, product quality, employee and community safety, air pollution control and many other aspects of operations. A water management strategy has to be an integrated view of water’s relationship to all of these issues. As a simple example, a decision to conserve water by not proceeding with a wet scrubber system which would improve air quality would be wrong. Dry options that could achieve the same air quality could however be part of a solution to both problems, and research into this could be incorporated into the strategy.  

It is ultimately the quantity and quality aspects of water management that are of interest. These issues are relevant for your own operations, those of your suppliers and those of the users of your products. In the latter instance, the water use of interest is that specifically associated with the use and disposal of your products. The questions to be answered by your organisation’s water management strategy (for your own operations, those of your suppliers and those of your customers) are broadly as follows:

·         Is there sufficient water available and what are the short, medium and long-term projections for water supply? This issue will clearly also impact on the cost of water;

·        What is the impact of acquiring this water on the environment, now and in the future? – if water needs to be pumped large distances to meet the needs of your operations, those of your suppliers and those of the users of your products, there could be a significant emissions component to the overall environmental footprint of the water use, for example;

·         Is the quality of the water available adequate and what are the business and environmental impacts for your organisation of incoming water quality? How is this quality changing over time?

·         How do your operations, those of your suppliers and those of the users of your products impact on water quality, and what is the impact on those who ultimately use this water?

·         In minimising your water use and mitigating impacts on other users, what are the potential negative impacts on other aspects of your operations?

Review of these questions gives the lie to common perception that only large water users require a water management strategy. Industries which use little water often have the potential to pollute large volumes of water by virtue of their effluent discharges (which may be small in volume but highly concentrated), or incur large water uses in areas of their product life cycles outside of their immediate processing operations.

What should be clear from the above is that in answering these questions and in devising the strategies necessary to ensure sustainable water use, you will need to engage with a wide range of stakeholders. These will include not only stakeholders in your supply chain and customer base, but also regulators, industry specialists, alternate suppliers, researchers, policymakers and of course other water users.

It is probably easiest to begin with your own operations and then broaden your strategy to include other stakeholders over time. The key issues should however initially be unearthed with a detailed risk assessment, which is a useful way of prioritising the appropriate course of action.

HOW COOLING TOWER EVAPORATION DRIVES WATER INTENSITY IN COAL-FIRED POWER GENERATION

Power generation is generally acknowledged as a water-intensive activity. Eskom, South Africa’s power utility, reports a specific water consumption of some 1.3 litre/kWh sent out to the grid, with a standard consumption target of 1.4 litre/kWh sent out for the organisation as a whole. The actual amount of water consumed at individual power stations depends strongly on the cooling technology employed. To understand the crucial role of cooling as regards water use efficiency in the power generation process, refer to the simplified flow diagram below.

In simple terms, coal-fired power stations burn coal in order to heat up demineralised water and produce superheated steam. This steam is then passed through turbines which convert kinetic energy in the steam into electrical energy. The steam emerges from the turbines at a lower temperature and pressure, and is then condensed before being pumped back to the boilers to produce yet more superheated steam in what is essentially a closed cycle.

The condensing of the steam is achieved in massive heat exchangers (condensers) using water as a coolant. The cooling water removes energy from the steam as the steam is de-superheated and condensed, and increases in temperature as a result. In some countries this warm water is discharged (once-through cooling) and may cause modification of the receiving environment due to thermal pollution (this depends on the capacity of the sink used). In South Africa, the warmed cooling water is instead cooled and reused.

The cooling device employed may be “wet” or “dry”, with “dry” cooling being the most efficient technology from a water use perspective. Dry cooling technology cools the warm cooling water through a process similar to that of the radiator in your motor car. The water is passed through a large heat exchanger, and air is passed over the heat exchange surface, either through natural draught or using fans.  The air is heated and the water is cooled. Eskom estimates that dry-cooled stations use 15 times less water than wet-cooled stations. It must however be noted that this excludes the use of flue gas desulphurisation technology, which could significantly increase water use at dry-cooled stations.

At power stations employing wet cooling systems, warm cooling water is passed over packing in a cooling tower. Air is passed up the tower in counter-current flow to the water. The surface area of the packing facilitates heat and mass transfer, and a portion of the water is evaporated, humidifying the air. Since this evaporation requires energy, the main body of water is cooled in the process. Fresh water has to be constantly added to the cooling tower to compensate for evaporation and blow-down losses. Blow-down water is typically recycled to other processes e.g. ash handling.

Evaporation is the the primary driver of water consumption at wet-cooled power stations, typically accounting for more than 80% of the water used. The conversion of existing wet-cooled power stations to a dry cooling system is technically possible, but would incur significant capital costs and introduce the potential for serious operational disruptions. It is therfore not really feasible. Dry cooling is however a real option for new power stations and is in fact already in place at a few South African power stations, such as Kendal, Matimba and Majuba Power Stations. Eskom has committed to the use of dry cooling for all new coal-fired power stations.

There is an interesting relationship between water use and energy efficiency at wet-cooled power stations. The energy contained in coal is expressed as its calorific value, which is in effect the amount of heat energy produced when a given mass of coal is completely burnt with oxygen. The efficiency with which this energy is converted into electrical energy depends on two primary factors:

• the efficiency with which the boilers convert the energy in the coal into energy in steam - given that in power generation coal is typically pulverised, and boiler controls are very sophisticated, efficiencies in excess of 90% are achievable;
• the efficiency with which the energy in this steam is converted into rotational energy at the turbines, and then to electrical energy  - this is limited by the thermodynamics involved and depends in part on the steam temperature and pressure. Values in the neighbourhood of 40% are typical, with higher efficiencies possible with supercritical boilers. 

Both boiler and turbine efficiency levels are important in terms of GHG emissions and power station operating costs. It is however turbine efficiency which is the ultimate driver of evaporative losses at wet-cooled power stations. The more efficiently the turbines operate, the less heat has to be removed by the condensers, and hence, for wet-cooled power stations, the lower the level of evaporation at the cooling towers.

Copyright 2011-2013, Craig van Wyk, all rights reserved

All information regarding Eskom from www.eskom.co.za