Clean Water for Farm to Use - Case Study Example

Clean water for farm use Table of Contents 3 Introduction 4 Discussion 5 Devices calibration 7 Management of sensors 9 Data capture and relay 10 The SCADA system 11 conclusion 15 References 17 Abstract A process control system monitors a water treatment environment and it electronically controls the process on the limits that are determined and set by the operators. The controlled system is usually part of the plant in which the controlled variables must be determined at the desired value and the variables that must be manipulated are used to compensate for the disturbance variables. Before a controlled can be used and incorporated into the system, the behavior of the controller must be known and defined so that the control system is able to focus on the response of the system. Introduction Farm water comes from a number of different sources and therefore its quality varies from one source to another. Water sources include dams, boreholes, wells, rivers and town water channels and recycled water. Water from various sources may be of an unsuitable quality for its intended purpose such as irrigation, stock, household or other farm activities. It is important that the correct water quality problems that affect the usage in the farm as well as the productivity of crops are identified. Water quality can have adverse effects on plants growing in the farm, soils, livestock present in the farm, irrigation equipment operational in the farm, water for domestic usage and the general farm activities. Farm water must maintain a certain level of the elements present beyond which the water has some adverse effects on the farm soil. 1. PH This describes the acidity or alkalinity of water. The PH of the soil can affect the growth of plants, irrigation equipment, pesticides efficiency and the quality of drinking water. Water that has a PH that is below 7 is acidic and that which has a scale above 7.5 is alkaline in nature. Most of the natural waters that exist are between PH 5 and 8. The accepted PH for farm water is 6.5-7.5. 2. Iron The iron bacteria will develop in water where the concentration range of iron is 0.3 to 1.5 mg/l. concentrations that are above 1.5 mg/l tend to favor the development of iron deposits. The irrigation systems that are used for fertigation should use water that has high iron content. 3. Hardness Water hardness is determined by the amount of calcium carbonate present. The table below shows the amount of CaCo3 that is present in each classification of hardness. Table 1: Classification description of hardness Classification description Hardness expressed as mg/L of calcium carbonate Soft Less than 50 mg/L Moderately soft 50-75 mg/L Slightly hard 75-150 mg/L Hard 150-300 mg/L Very hard Greater than 300 mg/L Hard water affects soil, stock and domestic water use, pipes and equipment. The farm water needs to maintain the following standards. Table 2: farm requirements for hardness Needs Hardness Dairy equipment and hot water systems Up to 150 Domestic use Up to 200 Dips and chemical sprays Up to 300 Septic tanks and hosing downs Over 300 4. Sodicity This refers to the measure of the amount of exchangeable sodium cat ions in water or in soil. In water, it is expressed as a sodium absorption ratio(SAR). If the SAR is greater than 3, the water is sodic and is a potential hazard in soils. It is important to consider water processing system design in the development of an efficient water treatment system. The treatment system must be designed with a number of fundamental water treatment processes. These processes include: coagulation, sedimentation, PH measurement and filtration process. Processes 1. Alarm design The proper management of water purification system is essential to the profitability of the farm. It is important that the parameters that are available in water are defined and we propose monitoring methods that will be used in the system. Table 3: available parameters and monitoring methods Parameter Monitoring method Frequency Alarm Dissolved oxygen DO meter Continuous + PH PH meter Daily - Carbon(iv)oxide Wet chemistry/PH meter As needed - Alkalinity Wet chemistry Everyday - Temperature Wet chemistry Continuous +/- TAN Wet chemistry Daily - Nitrites Wet chemistry Daily - Nitrates Wet chemistry weekly - Tanks water level Mechanical/electrical Continuous +/- Recycled water flow Mechanical/electrical Continuous +/- +=requires automated alarming -=does not require alarming +/-=optional It will be important that an alarm system is incorporated to monitor data during the process of water treatment. An alarm system will be designed to help the operators act quickly towards alleviating the needs arising in the system. It will incorporate the following aspects: a) The system will include the facilities for grouping, selecting and sorting out information. The information can be sorted according to time, operator on duty, area or the device that has the need. This will help the operators refer the alarms to the specific needs. b) It will have suppressing capabilities. The system should display relevant information every time. This will ensure that the information received each time is applicable for that particular process and thus avoiding the flooding of the alarms when great breakdown has occurred. It however, should not filter the alarms. This will ensure that all information necessary for the management of the water is received whether it belongs to the current situation or not. c) The alarm system will output alarms that are easy to understand. Operators should interpret the alarm displays to help them respond to the suppressed alarms while acting fast on the very urgent concerns. Emergency alarms should be displayed as critical hence acted upon by the specialties such as engineers. After installing an alarm system, there will be two main specifications to look for. The system should warn of abnormal situations with the water devices or level. It should thus inform the operator on whether to take a quick assessment or a progressive control action that will ensure continuous productivity and efficiency. The system will also serve as a reference log. The operator will be able to analyze the past behavior of the water devices and compare them to the present conditions hence take the necessary action. 2. Water treatment process In the water treatment system, a number of processes will be employed in the system from the point of water intake to the production of the final purified water. These processes are discussed below. 1. Coagulation This process begins with the pumping of the unclean water from the well or river. Adding alum to help in settling of the smaller particles and colloids. It is also used to reduce the negativity for the particles to come closer together. In this process, dirt and other particles that are suspended in water are removed. The alum forms sticky particles called floc which attract the dirt particles. The combined weight of the dirt and alum become heavy enough to sink to the bottom through sedimentation. In this section of the system, ultrasonic sensors can be used to monitor the progress of the process. These sensors use a transducer with a combined transmit and receive capability. The instruments measures the time it takes for sound to travel from the transducer to a target and then for the echo to return Advantages of using the ultrasonic sensors a) It provides information of high accuracy levels. b) It makes use of a no-acoustic sensor. Figure 1: ultrasonic sensor Table 4: data ranges for ultrasonic sensors Input Range:2.5-10 Output 1% of full scale Accuracy Range: 1% of full scale Power Supply 7-20Vdc Indication 5-character alphanumerical LCD indicator Temperature Limits -10°C to +60°C 0°C to +50°C Static Pressure Limit 0°C to +50°C Hazardous Area Certification Explosion proof and intrinsically safe Weight Industrial model: 86g Figure 2: flow diagram of the implementation of the coagulation process. 2. Sedimentation This process removes solids that settled individually and those from the coagulation. Water flows to the sedimentation basin where the force of gravity causes the floc to settle at the bottom. Large particles settle more rapidly than small particles. This section of the system contains turbidity sensors which measure the suspended materials in water. This is achieved by measuring the amount of light transmitted through the water. They are mainly used in points where gauging is of utmost importance. Advantages of using turbidity sensors a) They have self cleaning capability. b) They are field replaceable. c) The sensors are fouling resistant. Figure 3: turbidity sensor Table 5: turbidity parameters Input Range:4.5-7.5 FTU Output 1% of full scale Accuracy Range: 1% of full scale Power Supply 7-20Vdc Indication 4 ½-digit numerical Temperature Limits -10°C to +60°C 0°C to +50°C Static Pressure Limit 0°C to +50°C Hazardous Area Certification Explosion proof Weight Industrial model: 86g Figure 4: flow diagram of the implementation of the sedimentation process. 3. PH measurement This involves the measurement of the alkalinity or acidity of the water. The accepted PH ranges between 6.5 and 7.5. This section of the system has PH sensors which detect any changes in the Ph of the water. The PH sensors consist of a measuring electrode, a reference electrode, a temperature sensor, a pre amplifier and an analyzer or a transmitter. The PH measurement loop is usually a battery where the pointing terminal is essentially a battery. Advantages of using PH sensors a) It provides accurate data. b) It comes with a calibrated sheet for any adjustment. c) Its cables are replaceable in case of any damage or wear. 4. Filtration The filtration tank features a backwash system for washing the tank and removes particles that are clogged in the filters sand. Filtration process removes solids that were not removed through sedimentation. In the filtration section, a pressure sensor is installed into the system to monitor the flow of the filtered water and therefore maintain a proper pressure in the tank. Pressure sensors are typically 2 wired devices with each one of them transmitting a 4-20MA of current output with a 24VDC excitation. Table 6: pressure sensor parameters Input Range: 6.5-7.5 Output 4-20 mA Accuracy 2% full scale Power Supply 10 to 30 VDC Indication 4 ½-digit numerical and 5-character alphanumerical LCD indicator Temperature Limits 5° to +55°C Static Pressure Limit (7MPa) (725 Psi) Hazardous Area Certification Explosion proof and weather proof Weight Industrial model: 454 g Advantages of using pressure sensors a) They can be used in high solids applications such as different sludge levels. b) It gives a good accuracy of +- 1% of full scale. c) The pressure sensors can be calibrated by the manufacturer and customized to fit their intended purpose. Figure 5: pressure sensor Figure 7: flow diagram of the implementation of the filtration process. Table 6: parameters for pressure sensor Input Range :30-100 psi Output Two-wire, 4-20 mA (HART protocol) Accuracy Range 1: 30-100 Range 2:35-60 Power Supply 12 to 45 Vdc Indication 4 ½-digit numerical and 5-character alphanumerical LCD indicator Temperature Limits 23° to +131°F (-5° to +55°C) Static Pressure Limit 10,000 psi Hazardous Area Certification Explosion proof, weather proof and intrinsically safe Weight Sanitary model: 2.5 kg (5.5 lb.) Devices calibration This refers to the process of correcting the devices readings against a standard reading. The process of calibration is divided into two parts. a. Trimming of the range of the setting. b. Setting of the range This mechanism of separation allows the range to be changed without application of a physical input and this allows a huge saving on cost. 1. Trimming of the range of the setting: this is used to correct the digital reading as it is indicated in the device local indicator. This can be used to optimize the performance of the devices performance. There are three forms of devices trims available: a) Zero device trim b) Lower sensor trim c) Upper sensor trim 2. Setting of the range: this refers to the setting of the sensor. Normally, this is referred to as the calibrated range. Lower range values are usually referred to as zero while upper range values are called full scale. Management of sensors The very unfriendly and harsh environment within which the sensors are deployed may result into a biasness or a drift and even cause signals to fail. For proper management of sensors, it is important to have a system that allows timely diagnosis of the sensors. This can be achieved through a number of stages which will involve a number of processes including: a. Placement of sensors: this will ensure that the sensors are placed in the treatment tanks so as to capture data appropriately. b. Diagnosis of the sensors: this will help to detect any failures and faults. c. Prognosis of the sensors: this will focus on the future failures and faults in the systems. Data capture and relay After the data has been captured by the alarms and sensors, the SCADA has programmable Logic controllers and remote terminal units(RTUs) that are connected to sensors and they are able to convert sensors signals to digital signals which can then be analyzed using a control computer located in an office. Operation of the SCADA system After the necessary alarms and sensors have been identified, it is important that we come up with a supervisory control and Data Acquisition (SCADA). This system can be used to describe a number of computer based control systems and this gives operators and facility managers an opportunity to monitor a facility’s equipment either within a remote scope or a localized scope. This data is stored in a distributed database and can then be analyzed during the operation of the SCADA system. The SCADA system will therefore be used to create an automated control process so that the operators of the plant in question can be in a position to focus on other tasks. This will help the operators a chance to manually control the equipment that are contained in the system as they desire. SCADA systems can also be put into place for a number of reasons including collection and storage of information, for reporting, troubleshooting and maintenance indications. Advantages of installing a SCADA system a) It has the capability to significantly reduce the cost of operation while at the same time making improvements in the system performance making the system much more reliable. b) It makes it easier to avoid any afterhours call outs as the SCADA system is able to output and indicate the nature of the problem. c) Data is recorded on a continuous basis and therefore operators do not have to read and record the meter readings manually every day. d) Operators of the plant do not have to keep a record of the voluminous number of log sheets as any data that is recorded on the SCADA system can be downloaded and accessed any time as they wish. e) SCADA systems can be accessed remotely through connection to the internet using a Personal computer or laptop, phone or tablet in your home or office. 3. The SCADA system In the SCADA system created in the water treatment plant, water will be pumped in from a river or a well and it is redirected into a treatment tank where the processes of coagulation, sedimentation and filtration will be measured. Sensors will be installed into the system including ultra sonic sensors, turbidity sensors and pressure sensors. The data recorded will be relayed to a computer system that keeps track of the health of the plant. Valves will be used to control the flow of the treated water out of the plant. Below is a simplified representation of the SCADA system. Figure 7: SCADA representation of the treatment process. 4. System monitoring and data storage With an integrated system of SCADA, water management is achieved in the most efficient and effective technique. Predominantly, it is commonly used to monitor and control water from storage sites and pumping stations thus providing up to date information about the current status of the water facilities. The motors are used to manage quite a number of pumps and valves which can be supplemented with very sensitive temperature sensors to stop the possible reverse of water. Essentially, this system incorporates the use of combined switchboards with low voltage which enables the access of a centralized system of data as a result reducing the installation costs. Also, the use of Quantum Profile component in temperature sensors can be employed in order to regulate the flow meters. This is achieved when the level of water drops below the minimum level, the operator will be notified by the signal of the sensor and more water can be pumped to reach the maximum level. Air valves will drain away unrequired air in the water pipes thus ensuring ease of flow of water. Many benefits and merits accrue due to the use of this technology which among others will lead to reduced maintenance costs, development of more water supply, increase in revenue, reduction in water spillage and water conservation. Feedback mechanisms for control The mechanisms that are used to relay feedback in the system are used to manipulate the any information that is being input into the system and minimize the possible error. The feedback control will react to the information generated and will therefore strive to work towards reducing the error present by allowing the operator to input or correct the desired output. The system output which is measured by devices such as flow meters and the difference can be calculated and determined so as to reduce the amount of error that is present in the system. Figure 8: loop system of a control system. Advantages of automating the process of water treatment a. Automation makes the system more reliable as it has a more enhanced performance. b. The productivity of the treatment plant is more enhanced and the water quality and quantity is more improved. c. The system ensures that operation of the system is safe despite the mistakes that may be done by the operator. d. The system reduces the cost of operation in the treatment of water an there is a much reduction in the cost of operation and distribution of the water. e. The cost of maintenance is very low as the system can be operated by the normal staff and there is no need for complex spare parts. Conclusion From the discussion, it comes out clearly that an automated system for treatment of water would be of great importance as this will greatly reduce the cost incurred in the operation of the water treatment plant. Having an automated system improves the efficiency and quality of water treated for use in the farm and this makes operations in the farm much more efficient. The SCADA system that is generated can be used to monitor the farm activities remotely and therefore the system can be monitored from the office or from the house using a laptop or phone that is connected to the internet. References "Climate Information for South Dakota." Climate Zone. 2003. Cia World Fact Book, retrieved from. 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