Data Acquisition System for Gas Monitoring in Landfills

8/6/2019 Data Acquisition System for Gas Monitoring in Landfills

http://slidepdf.com/reader/full/data-acquisition-system-for-gas-monitoring-in-landfills 1/10

ICCBT 2008 - D - (34) – pp363-372

ICCBT2008

Data Acquisition System for Gas Monitoring in Landfills

F. N. M. Fauzi, Universiti Tenaga Nasional, MALAYSIA

N.A. Abu Bakar , Universiti Tenaga Nasional, MALAYSIA T. Syed Jalal , Universiti Tenaga Nasional, MALAYSIA N. Md. Din *, Universiti Tenaga Nasional, MALAYSIA

ABSTRACT

Landfill energy extractions comprise of a large number of gas wells used to yield the gasmethane for electricity generation. These wells are dispersed over a large land area. Tomanage the gas wells manually would require visiting each one of the wells to inspect theconditions of the wells. This paper describes an effort to develop a data acquisition

framework for a centralized gas monitoring system in landfills for a location in Malaysia. It describes the options of utilizing sensors, signal conditioners, communication links and

centralized consoles. Initial development of the data acquisition system and signalconditioning circuit using LABVIEW are presented.

Keywords: Landfill, Data acquisition system, Gas monitoring, Sensors, Signal conditioning.

*Correspondence Authr: Assoc. Prof. Dr. Norashidah Md Din, Universiti Tenaga Nasional, Malaysia. Tel:+60389212395, Fax: +60389212116. E-mail: [email protected]

http://www.uniten.edu.my/newhome/content_list.asp?contentid=4017




ICCBT 2008 - D - (34) – pp363-372 364

1. INTRODUCTION

Worldwide, mankind produces an abundant amount of wastes where the handlings becomeincreasingly difficult with time as the world’s population grow and land becomes limited and

more expensive. Improper waste treatments also pose hazardous impacts to the ecology,environment and health. With these effects in mind, the concept of waste to wealth is on therise where waste can be made into useful materials and energy sources to promote good wastemanagement. The next figure shows the massive supply of waste available in Malaysia to betapped for energy.

Table 1. The annual amount of waste in Malaysia [1]

Year Population Estimated amountof waste

(Tonnes/Year)1991 17,567,000 4,488,3691994 18,917,739 5,048,8042015 31,773,889 7,772,4022020 35,949,239 9,092,611

Landfill is a common solution for Municipal Solid Waste (MSW) management in Malaysia.In landfills, methane is naturally produced through anaerobic process in the MSWdecomposition. Besides methane, landfill gas is composed of a mixture of hundreds of different gases. By volume, landfill gas typically contains 45% to 60% methane and 40% to60% carbon dioxide. Landfill gas also includes small amounts of nitrogen, oxygen, ammonia,sulfides, hydrogen, carbon monoxide, and nonmethane organic compounds (NMOCs) such astrichloroethylene, benzene, and vinyl chloride. Since the MSW degradation process is anatural and spontaneous process, the amount of methane varies from time to time, dependingon the external factors that influence the chemical process.

A centralized monitoring system for gas wells monitoring and gas composition monitoring isproposed in order to ease the operations in collecting the methane at landfills. The methanelevels in wells are to be monitored using appropriate sensors. The wells are to be clustered to

a data acquisition box and a Wirelass Local Area Network (WLAN) access point. WLANcommunications will then be made between access point and centralized monitoring stationlocated at the main office. The centralized monitoring station will be the focal point fordatabase management and escalation process. The escalation process includes sending shortmessage service (SMS) messages to the person-in-charge.

2. DATA ACQUISITION SYSTEM

Data acquisition is the process of gathering or generating information in an automated fashionfrom analog and digital measurement sources such as sensors and devices under test. Data

acquisition uses a combination of PC-based measurement hardware and software to provide a



F. N. M. Fauzi et. al.

ICCBT 2008 - D - (34) – pp363-372 365

flexible, user-defined measurement system [2]. The hardware part is made of sensors, cables,signal conditioning, data acquisition card. The software part is made of the data acquisitionlogic and the analysis software and some other utilities that can be used to configure the logicor to move data from data acquisition memory to the central console.

In this work, a data acquisition system [3] for gas monitoring was designed using LABVIEWsoftware. Several monitoring specifications have been identified in order to design themonitoring system. The specifications include methane classification and factors that affectthe landfill methane gas production rate. Methane classification is shown in Table 2 below.

Table 2. Methane Classification0% - 5% 5% - 15% 15% - 60%Failure

(both lightsturn red)

Need Checking(1 st light turns

red)

OK

Figure 1. Block Diagram of the Monitoring System

Figure 1 illustrates the block diagram layout of the monitoring system. This program utilizedthe g-programming language by LABVIEW. This monitoring system is designed byconsidering one of the factors that affect the methane production rate in the landfill which istemperature.

Methane production rate is directly proportional to the change of temperature. As thetemperature decreases, the methane percentage also decreases. Based on figure 1, it can beseen that the block diagram consists of two simulated signal components which generate

signals for the thermometer and the methane percentage meter. In this program, the knob is




ICCBT 2008 - D - (34) – pp363-372 366

used to represent the input and to adjust the increment and decrement in temperature. Theknob represents the gas sensor. It is connected to the first simulated signal component toincrease or decrease the temperature which is in the range of 20ºC to 80ºC. At landfill thetemperature is approximately 40ºC to 60ºC, but in this design, average value is used as the

initial temperature which is 50ºC. The temperature is then displayed on the temperature graphas well as the thermometer to improve the readability.

The second simulation signal component represents the methane percentage. The value of themethane is displayed using the meter and also the value is displayed numerically. In thegraphical programming, comparison Boolean is used to ensure that the light will turn red atcertain condition according to methane classification. At the same time, when the value of themethane is within 5% to 15 %, the first light will turn red indicating that the system needschecking. When the methane percentage goes below 5% then both light will turn redindicating the system failure. The typical value of methane at landfill is within 54% to 60%.

Figure 2. During normal Condition

Figure 3. Failure Condition




ICCBT 2008 - D - (34) – pp363-372 367

Figure 4. Need Checking Condition

3. OPTICAL GAS SENSOR

Optical measurements are the most accurate and reliable method for gas analysis. Optical gassensors [4] depend on measuring the transmission of light at different wavelength for eachgas. The particular wavelength identifies the gas and the amount of light absorbed by the gasdetermines the gas concentration.

Figure 5. A Basic Fiber Optic Sensor System

Figure 6. Absorption of Common Gases

The concentration of methane in landfill gas can be monitored by using an optical gas

detection system. The methane will be absorbed by a gas absorption cell. A light source at a




ICCBT 2008 - D - (34) – pp363-372 368

specific wavelength is passed through the cell and interacts with the absorbed gas. Thereturned light is then examined to determine the amount of power absorbed by the gas cell.This is then translated into the concentration of methane gas.

A multiplexed system can be used to monitor multiple wells simultaneously. One singlesource can possibly be used to power up all gas absorption cells. An intelligent dataacquisition can collect data and send it to a central processing computer for data storage andanalysis. The connection from the source to the each individual well is made using a normalfiber optic cable.

There are several methods of methane gas detection over optical fiber paths that can be used[5]. One of them is by using a broadband white light source and a rotating-chopper/interference-filter arrangement to sequentially interrogate the transmission of thesample cell, over the desired fiber optic cable link. Semiconductor LED sources can also beused in conjunction with a fiber-remoted methanometer. The useful power that can beextracted from a broadband incandescent or LED source can be increased by using Fabry-Perot cavity having the wavelength spacing equal to that between each of the rotationalabsorption lines of methane gas.

Figure 7. Absorption Spectrum of Methane

4. OPTICAL SENSOR IMPLEMENTATIONS

Basically, there three are types of optical sensor implementations as shown in Figure 8 [6, 7].They are:

1. Point sensor.The measurement is carried out at a single point in space, but it is possible to usemultiple channels to address multiple points.




ICCBT 2008 - D - (34) – pp363-372 369

2. Distributed sensor.

The parameter of interest is measured with a certain spatial resolution at any pointalong a single optical cable.

3. Quasi-distributed sensor.The measurand is determined at a number of fixed, discrete points along a singlefiber optical cable.

Figure 8: Optical Sensor Implementation [6, 7]

5. FIBER OPTIC METHANE SENSOR

Figure 9 shows the components of fiber optic methane sensors [8]. White light and opticalfilters are used to measure methane concentration using differential absorption techniques.The gas concentration is determined by the amount of light absorbed by the gas. Detectorsthat are located behind each of the filters convert the light into electrical signals that areprocessed to calculate the concentration of methane present in the gas cell.

Figure 9. Fiber Optic Methane Sensor




ICCBT 2008 - D - (34) – pp363-372 370

6. ADVANTAGES OF OPTICAL SENSORS

Optical sensors have significant advantages compared to conventional sensor types, in termsof their properties. Following are the advantages of optical sensors [9-11]:

• Immune to electromagnetic interference (EMI), cross talk and space radiation.

• Completely passive• Small size, light weight, low cost, low power.• High sensitivity, large dynamic range and resolution• Remote operation over several miles length without any lead sensitivity• Can measure a large number of points along a single optical cable.• Can monitor a wide range of physical and chemical parameters.• High temperatures resistance.

7. SIGNAL CONDITIONING

Usually the output of a sensor is only in the range of milivolts. The signal is not strong enoughto pass through to the data acquisition system. Therefore, signal conditioning is needed toamplify the output sensor so that the data acquisition can process the data.

Figure 10 shows the schematic of signal conditioning circuit that had been designed for thecentralized gas monitoring system. Meanwhile, Table 3 shows the results obtained from thecircuit simulation. From the results, we can see that this signal conditioning amplify theoutput sensor with a gain of 10 [12].

Figure 10. Signal Conditioning




ICCBT 2008 - D - (34) – pp363-372 371

Table 3. Sensor Outputs after Amplification

8. CONCLUSION

By developing a data acquisition system for centralized gas monitoring in landfills, themanpower can be reduced. Besides that, accurate results can be obtained with reduced humanerrors.

Taking advantage of the capacity of optical fibers to send and receive optical signals over longdistances, it shows that using optical sensor for gas monitoring is a viable solution for thecentralized monitoring system. By using optical sensors, it is not necessary to convert betweenelectronics and photonics separately at each sensing site, and thereby reduces costs andincreases flexibility.

REFERENCES

[1]. Mazlinda Hashim, "Present Status and Problems of Biomass Energy Utilization inMalaysia", APECATC-Workshop on Biomass Utilization, 19-21 January 2005 inTokyo and Tsukuba, Pusat Tenaga Malaysia

[2]. Data Acquisition (DAQ), National Instruments, 2008

[3]. Nurul Akmar Abu Bakar, "Data Acquisition Software for Centralized Landfill WellsMonitoring", Final Year Thesis, Universiti Tenaga Nasional, 2008.

[4]. Mary Jane Perry, " Optical Sensors " , School of Marine Sciences and Ira C. Darling

Marine Center, University of Maine, 2003, white paper.

[5]. Dr. J P Darkin, " Optical Fiber Gas Sensors " Review Paper, Optoelectronics ResearchCentre, University of Southampton, SO17 1BJ UK, SPIE 102, paper 27.

[6]. Dr. Rudiger Paschotta, " Fiber Optic Sensors " , Encyclopedia of Laser Physics andTechnology, RP Photonic Consulting GmbH, 2008.

[7]. Paul E. Sanders, " Optical Sensors in the Oil & Gas Industry " , WheatherfoldInternational, Slide Presentation, 2004.

Input (mV) Output (V)480.5 4.805532.2 5.322633.8 6.338710.6 7.106789.2 7.892822.6 8.226




ICCBT 2008 - D - (34) – pp363-372 372

[8]. Thomas H. Dubaniewicz, Joseph E. Chilton, and Harry Dobroski, Jr., "Fiber Optic forAtmospheric Mine Monitoring", IEEE Transactions on Industry Applications, Vol. 29,No. 4, July/August 1993.

[9]. A. Selvarajan, Fiber Optic Sensors and Their Applications, Department of ElectricalCommunication Engineering Indian Institute of Science, Bangalore, 2000.

[10]. Nina Morgan, " Let There Be Light " , Frontiera, April 2002.

[11]. Dr. Colin Fitzpatrick, “Optical Fiber Sensor…The Other Optical Revolution!!”Elements, Issue 6, May 2006.

[12]. Fara Nadiah Mohd Fauzi, "Monitoring System for Landfill Gas (LFG) PowerGeneration in Malaysia: Gas Monitoring System"; Final Year Thesis, Universiti TenagaNasional, 2008.

Documents

Data Acquisition System for Gas Monitoring in Landfills