Case Study, Upgrade of the mixing plant (PART 1)

INTRODUCTION

My proposed project is on the upgrading and automation of Creamer mixing plant at Entyce Beverages, one of the South African plants is in Kempton Park, Isando. Entyce Beverages manufactures Ellis Brown creamer and is one of the fast-moving creamer products in the whole of Southern Africa. The process of mixing reamer ingredients will be automated together with the feeding system. Product measurement will also be upgraded to cater for electronic batch storing of information.

1.1   THE BACKGROUND TO THE PROBLEM

The Creamer mixing plant

• The Creamer mixing plant is now old and outdated because:
  • The wiring is old and insulation resistance has dropped significantly due to the damage caused by rats and temperature variations.
  • Some of the wiring diagrams have missing pages due to multi handling and there is no way of getting the missing pages.
  • It is using old components and technology which is now difficult to find on the current market.
  • The wiring has lost its labels which makes it difficult for fault finding hence increased downtime.
  • The panels have rusted on the bottom, so the armoured cables are falling which causes a great danger due to loose earthling.
• The plant is too manual hence it requires a lot of people for monitoring hence it difficult to trace nonconformity.
• There is no history which is kept after the batch has been made; all entries are recorded manually which leaves room for human error.
• The process is run manually; raw materials are fed manually which mean they can be measured wrongly.

Due to the above problems, the author will help with the assistance of Engineers, Artisans, Suppliers, Department of Labor, SHEQ Department and project department has been asked to help with the designing and implementation of an upgraded and automated mixing plant. The plant would meet the following requirements:

1.2  USER SPECIFICATIONS

The user requires a plant which will satisfy the following criteria:

• Must be repairable i.e., use components/parts which are readily available on the market
• Must have wiring diagrams which are soft copies and hard copies which stay in substation.
• All cables and components should be marked and neat. Different colour codes should be used to indicate cables carrying different voltages i.e., 230v and 24v
• The installation should have required insulation resistance as stated by SABS standard.
• Motor insulation resistance
• Insulation resistance between cables
• Earth loop impedance.
• Insulation resistance of the measuring instruments and the IP ratings.
• It must have lockable panels with keys enough to give to each trained service personnel.
• It must have required motor protection, overload, and overheat protection.
• Measurements of volumes must be done continuously, and the history should be kept.
• Ingredients must be measured during pumping and must be accurate.
• Must indicate if motor stops, trips, or overloaded.
• The motor must stop if shaft breaks on the agitator.
• Must not allow the process to start if all the conditions are not met.
• Must indicate valve statuses [open/close] and not take time to open or close valves.
• Must give alerts when there is a fault in any section of the mixing plant.
• Must be able to retrieve batch process history or generate reports.
• Must have a user-friendly Graphical User Interface (GUI).
• Must be reliable and user friendly.

The following environmental conditions/constraints apply:

• The plant mixes the creamer for all drying towers, there for it must not stop production during upgrading.
• Power available in control room is 220V /380V 3-phase
• Frequency 50 Hz
• Electric motors use 3-phase 380V power
• No direct current
• Power is available in the control room
• Temperature probes
• Contaminated rubbles and dismantled equipment must be thrown to licensed hazardous land fill zones.
• Materials which can be recycled should be thrown in their respective marked bins.
• All hot work and cutting should be done after getting a license for authorisation from the SHE department.

1.3  LITERATURE STUDY

A powder particle generally consists of a continuous mass of amorphous lactose and other components in which fat globules, casein micelles, and serum proteins are embedded. The manufacturing and mixing of those components or ingredients involve quite a complex process and is formed by a number of phases from measuring to the final storage. In order to produce quality milk, these processes or phases need to be done with precision and timely. The old methods do not meet such, hence the plant needs to upgrade to meet the technological changes in the world

1.3.1  AUTOMATION

According to Wikipedia, Automation or automatic control is the use of various systems for operating equipment such as machinery, boilers, and heat-treating ovens, switching on telephone networks, steering and stabilization of ships, aircraft and other applications and vehicles with minimal or reduced human intervention. It involves application of various control systems to enable operation of equipment to be carried out on their own with little human intervention. The term automation was not widely used before 1947, when Ford established an automation department. It was during this time that industry was rapidly adopting feedback controllers, which were introduced in the 1930s. Earl development was using relay logic until special computers called Programmable Logic Controllers (PLC) were designed to replace these collections of hardware with a single, more easily re-programmable unit.

1.3.2   REASONS FOR AUTOMATING THE OPERATION 

         Automation of an operation has the following advantages:

• Reduced operation costs: eliminates many of the costs associated with manual processes, not only in terms of wages but also training and administration.
• Improve product quality and consistency: automated systems produce consistently high-quality output. It provides accuracy and repeatedly exacting work done the same way each day and every time.
• Improve the work experience for employees: Automation makes things better employees working in an operation by executing repetitive, physical and most dangerous tasks.
• Increase production rate, wastes less and increase yields: It runs as many shifts as wanted and does not tire or take breaks
• Reduce capital costs: reduce the cost of consumables and waste. The employer is able to predict the production rate and ensure faster and efficient outcome with lower inventory levels.

Contrary to the above, automation also has the following disadvantages:

• Less versatility: by having a machine that can perform a certain task limits the flexibility and variety of tasks that an employee could do.
• Large initial investment: automated machines can be the costliest operation to the company.
• Increase in unemployment: By increasing the amount automation there are fewer employees required causing high employment rate.
• Unpredictable costs: there may be several unpredictable costs that may exceed the actual cost of automation. Some costs will include research and development cost of the automation process, preventative maintenance costs and cost of training the employees to operate the automated machines.
• A skilled maintenance department is required to service and maintain the automated system in proper working order. Failure to maintain the automation system will result in lost production and or a bad product.

However, after considering the above the technician noted that the advantages weighed far more than the disadvantages, thus automating the process was the better way to go.

1.3.3   PROGRAMMABLE LOGIC CONTROLLER [PLC]

It is a digital computer which has been adapted for the control of manufacturing processes. The PLC is designed for multiple input and output arrangement. It is designed to withstand the harsh conditions which can be in the processing plant. It is mainly used to any activity in the plant which requires high reliability control and ease of programming and process fault diagnosis. Programs to control machine operation are typically stored in battery-backed-up or non-volatile memory. It also allows its operation to be monitored and the output results must be produced in response to input conditions within a limited time.       

1.3.4   PUMPS AND MOTORS

To upgrade and automate the current motor control and protection, Variable Speed Drives (VSD) will be employed. The various types of industrial motors that can be used with VSDs are:

• Dc motor: dc motors are still in production although the number of active manufacturers has decreased considerably.
• Ac asynchronous squirrel cage motor: This type of motor is the most commonly used motor in industrial processes.
• Ac asynchronous wound rotor motor: This type of motor was traditionally used when the load required a high starting torque, and the strength of the power supply network was insufficient to permit Direct On-Line (DOL) starting. Variable speed operation is obtained by varying the effective resistance in the rotor circuit.
• Ac synchronous motor with brushless ac or brushed excitation.
• Ac synchronous motor with permanent magnet excitation: This type of motor is specifically designed for operation with a VSD.

1.3.5    CHARACTERISTICS OF VSDS (variable speed drives)

• Speed Control
  • A fundamental function of a VSD is to adjust the speed of an electric motor. The basic command frequency for VSDs is normally from 0 Hz to 50 Hz, but mostly with the capability to be adjusted up to 400 Hz. If the base frequency of a motor is 50 Hz then the final speed will be 8 times the base frequency of the motor with the command frequency set at 400 Hz.
  • Due to VSDs design, it is not practically normal for standard induction motors to operate at these high frequencies. In practice a command frequency set point of between 25 Hz and 75 Hz is acceptable without compromising performance or introducing any mechanical damage to the motor. At low frequency set points, care must be taken that there is enough cooling for the motor produced by the mechanical fan.
  • At high frequency set points, mechanical failure may occur due to the mechanical design of the motor bearings normally rated at the design speeds of 2, 4, or 6 poles. At high frequency command speeds, care should be taken as torque loss may be experienced.

• Torque control
  • Basic torque control is possible in an open loop system; however, the actual system response required must be considered. In an open loop system, the VSD monitors the motor current and adjusts the voltage to perform torque control, depending on the installation. If the current of the motor does not vary sufficiently, very inaccurate results will be obtained.
• Smooth controllable starting and stopping
  • A Simple adjustment of the time required to accelerate the motor from rest to full speed (Starting), normally 50 Hz, and from full speed to rest (Stopping), ensures a smooth controllable start and stop sequence. This reduces mechanical wear on the machine. Various types of starting and stopping curves are available by setting the correct parameters in the VSD.
• Energy saving
  • It is that a Direct-On-Line (DOL) starter will supply full voltage to the motor at the supply frequency with the current uncontrollable. The motor will use as much current as the load requires - normally between 600 to 700% of the full load current of the motor. Before the days of Soft Starters and VSDs the alternative to control the starting current was with Star-Delta starters, which reduced the starting current to approximately 200%.
  • The current limiting features on VSDs ensure that when a motor accelerate from rest, it will not exceed more than 100% of the full load current of the motor. Replacing DOL starters with VSDs will reduce the Current Demand when starting motors. VSDs will deliver maximum torque at the motor shaft while limiting the current to the full load current setting of the motor in the VSD.
  • If the efficiency of the system can be improved the power demand drops proportionally with the increased efficiency.
• Flexibility
  • The flexibility to set up and configure a VSD for various applications, e.g., Constant torque, Variable torque, Hoisting and many others, allow users to customise units to suit their needs.
• User friendly
  • Most VSD are supplied with basic LCD or LED display keypads, with which the user can adjust parameters such as acceleration time, deceleration time, full load current, etc. This allows the user to customise the inverter for his application. Most VSDs have advanced units that could copy parameters from one unit to another. Apart from this basic function, most units available today are supplied with serial communication ports to interface with personal computers that allow users to analyse the behaviour of their system.
• Ability to interface with other intelligent control system
  • Our demanding society forces managements to know what is happening in their plant and processes. Information from VSDs is not only for the engineer’s benefit, but also allows managements to see if they could increase their production safely without overloading the process or plant. This is normally done via the serial interface. It is also possible to integrate units into a complex network system.

• Mechanical wear and tear
  • It is to the advantage of the users that where mechanical wear is part of the process, users could speed up or slow down their application to deliver the necessary production.
• Audible noise
  • Various stages of the switching frequency produce audible noise from the motor. Although this is not harmful to the motor, in most instances the noise is not acceptable. The noise is unpleasant and irritating in quiet offices, hospitals and other such environments. To overcome this problem most VSDs’ switching frequency could be increased to a higher value, which will eliminate the noise problem, but this will introduce harmonics. Therefore, proper design of an installation should be done before using VSDs.
• Installation
  • VSDs are built with sensitive electronics components and must be installed in a clean environment where there is adequate air cooling and dust control.
• Supply Voltage
  • Always ensure that the correct voltage is available. In many cases user’s interpretation of a VSD is that you could supply the unit with single-phase 220V AC and control a three-phase motor rated for 380V AC. Most standard induction motors could operate with three-phase 380V AC with all six leads from the windings available and connected in a Star configuration. The same motor could operate with 3 Phase 220V AC if the leads from the windings are connected in a Delta configuration. However, consult the motor manufacturer if it is not indicated on the motor nameplate.
• Kilowatt size
  • It is not totally correct to select an inverter according to motor capacity in “kW”. It is better to select an inverter based on the rated current of a motor. If the inverter and the motor have the same capacity (kW), an increase in the number of motor poles reduces the efficiency and power factor of the motor increasing the rated current value.