CHAPTER I INTRODUCTION

Domestic sewage sludge can be defined as soft sludge and slimy sludge produced from sewage. The objectives of this project are to determine the energy recovery potential of sludge from domestic sewage treatment plants and to calculate the amount of energy that can be obtained from daily sludge disposal. This project focuses on the characterization of secondary sewage sludge and the amount of energy recovery on a Feed-in-Tariff (FiT) basis.

It was found that the heating value of secondary sewage sludge is time-dependent: the energy content was reduced by more than 1 kJ/g after 7 days. Based on this finding, it is not recommended to use secondary sewage sludge for energy recovery after 7 days. Energy recovery from sewage sludge is becoming very important as it can reduce the environmental impact of sewage sludge disposal and minimize the amount of sewage sludge to be landfilled.

Therefore, the study of the potential of obtaining energy from sludge from domestic sewage treatment plants becomes a good option for green technology and reducing the operating costs of the sewage treatment plant. Therefore, Malaysian sewage sludge needs to be characterized as a function of time before considering its energy potential.

Figure 1.1: Flow chart for sludge handling

Problem Statement

Objective

Scope of Study

Energy Policies

CHAPTER2

LITERATURE REVIEW

Sewage Sludge Combustion

To determine the potential energy recovery, several parameters must be considered for the suitability of sewage sludge as a fuel or energy source: for example, moisture content, heating value and the chemical properties obtained from proximate and ultimate analyzes [15]. The heating value of sewage sludge for treatment plants in Canada is shown in Table 2.1[16]. A mathematical model, based on chemical composition, to predict the heating value of domestic sewage sludge (DWS) in Thailand was proposed by [17].

The results confirmed that the composition of sewage sludge is mainly composed of volatile matter and ash in the range of and the overall composition of the sample. The amount of bound carbon was measured to be about 11.8% of the chemical composition of the sample, and the heating values ranged from 4000 kJ/g to 14,000 kJ/g. According to Jianguo Jiang, Xuejuan Du, and Shihui Yang (2010), a study on the combustion characteristics of domestic sewage sludge (DWS) using the thermal gravimetric method for samples collected in China, the dry basis calorific value was found to be 10.8 kJ/g , which is about half of the published value of low-grade coal.

The solid carbon content in the total composition of the sludge samples was found to be 3.48%, a relatively low value for fuels, while the volatile content was 43.67%, an amount that can help promote efficient combustion. Based on the literature search, there are variations in the results for the heating value and chemical composition.

Table 2.2: Heating value from various sources of biomass [19, 20, 21]

Research Methodology

CHAPTER3 METHODOLOGY

CHNS 2.3 TGA

Experimental

Removal of Moisture Content in Secondary Sewage Sludge

Before any experiment can be performed on secondary sewage sludge, it must be dried to remove the moisture content. After a few hours, the weight became constant, which meant that all moisture content was completely removed during this process. The sample was then kept in a plastic bag to protect the sample from moisture in the air.

It was very important to ensure that the samples were free of moisture before any experiment could be done on the samples. In order to reduce error, each sample was analyzed twice, and the average reading of the two experimental runs is reported. Before measuring the heating value for secondary sewage sludge, a standard sample was used to determine the variance between actual results and theoretical results.

The final analysis involved the use of a CHNS analyzer (Leco CHNS-932, VTF-900) to determine the elemental composition of the carbon (C), hydrogen (H), nitrogen (N) and sulfur (S) content of the sample. Samples were prepared in small tin capsules with a sample mass of 1.5 to 2 mg each. The result of this final analysis is important for calculating the boiler efficiency and in determining the stoichiometric equation for the combustion of secondary sewage sludge as a fuel.

Figure 3.4: (Left) The oven used for drying, and (right) the dried secondary sewage sludge

Proximate Analysis

CHAPTER4

RESULT AND DISCUSSION

Pie Chart for Proximate Analysis

CHNS Composition

Initial Moisture Content

Referring to Figure 4.4, the initial moisture content of secondary sewage sludge in Malaysia ranges from 80-90%. The secondary sewage sludge is completely dry when the weight measured during the drying process in the oven is constant. This initial moisture content value is very important to calculate the energy required for the drying process.

Since the best sludge handling for energy recovery is during the first 7 days after the dewatering process, this research has been focused on the heating value for this period. The mean calorific value for this period is 15.54 kJ/g with the highest uncertainty value of ± 0.19 kJ/g.

Table 4.1: Heating value for different time period

Comparison of Heating Valne with time

Heating Value Distribution

Prediction of Heating Value
Energy Balance for Power Generation
Feed in Tariff Calculation
Conclusion

For comparison between the predicted heating value and the measured heating value for high heating value (HHV), an empirical equation I is used and the percentage variation of the result is calculated using equation 2 developed in [17]. For the dried sludge sample used in this work, the volatiles content is 49.5% and the solid carbon content is 21.9%. Although the sample was thought to be completely dry, as indicated by the constant weight, there was still 0% moisture content in the dried sample, as shown by the adjacent analysis result.

During the drying process the sludge mass was weighed until it was constant to ensure that all moisture content had been removed. However, there was a possibility that the moisture content in the air affected the result of the proximate analysis. For best results, this experiment should be done in a dry environment where the moisture content is low so that there are small differences in the predicted and measured heating values.

The result was compared with previous work by another researcher and found that the calculated variation was still within the range reported in [7]. Once the sludge is dried, it can be used as fuel in a boiler to heat water and produce steam that is fed to a steam turbine. In this study, a 2 MW steam turbine was used as the minimum target power output to calculate the mass fuel burnup rate for sewage sludge.

This was taken from a literature review [23], since to calculate the boiler efficiency, a proper sewage sludge incineration boiler must be constructed and the sewage sludge combustion product must be analyzed with a gas analyzer. Therefore, the daily total weight of sludge to be removed, which is about 60,000 kg, can be used to generate 2 MW of electricity for about 10.6 hours at a mass fuel burn rate of 1131.12 kg/hour. According to the proximate analysis, although the sludge was kiln-dried to a constant mass, there was still about 10% moisture, which cannot be neglected and is associated with the dried sludge.

This 10% will therefore be taken into account when calculating the capacity for sludge drying. On a daily basis, a total of 60,000 kg of secondary sludge is generated by a steam turbine. Therefore, the energy recovery will help to reduce the cost of processing sewage sludge, especially in sludge disposal.

CHAPTERS

CONCLUSION AND RECOMMENDATION

It is recommended to construct a boiler and burn the sludge sample in the boiler and analyze the combustion product with a gas analyzer to determine the percentage of the product. Using data from the final and proximate analysis, here is a calculation of the boiler's combustion efficiency. In addition, there is also a method called torrefaction, which is a heat treatment process at a certain temperature range for a certain period of time, which can ensure low moisture content and increase energy density.

17] Puchong Thipkhunthoda, Vissanu Meeyoob, Pramoch Rangsunvigita, Boonyarach Kitiyana, Thirasak Rirksomboon, "Prediction of Calorific Value of Sewage Sludge in Thailand from Proximate and Finite Analyzes," Fuel, May 2005 [18] Jianguo Jiang, Xuejuan Du, Shihui Yang, " An Analysis of Sewage Combustion. 19] Ayhan Demirbas, Potential Uses of Renewable Energy Sources, Biomass Combustion Problems in Boiler Heating Systems and Combustion-Related Environmental Issues. 25] Kementerian Tenaga, Teknologi Hijau dan Air, Handbook on Malaysia's Feed-in Tariff to Promote Renewable Energy , 20 II.

Appendices

Be sure to use gloves, jacket, shoes, face shield and proper tools when handling hot materials and equipment. A cotton thread is fixed with a loop in the middle of the ignition wire and placed in the decomposition container. As soon as the system starts the experiment, a graph of changes over time in the ship appears on the screen.

When the measurement is finished, the decomposition is removed, cleaned and prepared for the next experiment. The sample is transferred to the DSC holder on the left side, the right side is reserved for the reference sample. In the Pyris I DSC program the "Method Editor" window is selected and the required parameters are filled.

The initial temperature is set and Go to temperature is pressed and the initial temperature is expected to be reached. After operation: The power switch, air and water supply are turned off and the equipment is cleaned. Leak Check is performed if necessary (the gas must be in the 'Analyze' position before a Leak Check can be performed).

The Auto/Manual switch is set to auto when using the carousel or to manual to load samples individually.