Waste Heat Recovery in Food and Drinks Industry (Abstract only)

Most baking processes in the food manufacturing sector involve use of gas-fired ovens. Only about one-third of the total energy used in these ovens adds value to the final product. The remaining two-thirds is discharged with the exhaust gases at 150-250o C and thus represents an opportunity for heat recovery. However, the low temperature range, fouling and presence of corrosive materials in the exhaust streams make heat recovery technically challenging and uneconomical. The existing low grade heat recovery technolgies mostly use gas to liquid heat transfer to produce hot water for use in other areas of the manufacturing plant. The performance of these systems is governed by hot water demand in the factory and is therefore not recommended if there are frequent fluctuations in demand or if a more efficient technology, such as combined heat and power, is already in place. This study involves design, manufacturing and testing of a novel low-temperature gas to gas heat recovery system using an array of heat pipe heat exchangers, for industrial-scale baking ovens at a large confectionary manufacturing plant. Unlike gas to liquid heat transfer, a gas to gas heat transfer system provides direct savings in oven fuel consumption, independent of the hot water and other energy demands elsewhere in the plant. The heat recovery potential of the system is estimated using a thermodynamic model developed based on energy and mass balance for the ovens. The design enables recovery of up to 50% of the energy available through the exhaust stack, increasing the energy efficiency of the overall process to 60% and reducing food manufacturing costs by one third

Techno-economic feasibility of a hybrid power generation system for developing economies

This work investigates the feasibility of hybrid power generation system using multiple energy sources to fulfil the electrical demand of a residential community. The system performance is evaluated against the capital investment, Cost of Electricity (COE), CO2 emissions and Net Present Cost. Results indicate that the hybrid system reduces the COE by 47% compared to grid price and has a negative CO2 emissions of 24,603 kg/yr due to supplying its surplus energy to the grid. Renewable sources contribute to 80.1% of the overall power produced by the hybrid system. The study finds that the hybrid systems could replace complete dependency on grids

Review of Waste to Energy Projects in Developing Countries

Waste to Energy (WTE) projects have been running successfully in many countries but have produced only mixed results in developing and have often been plagued with controversies. This is due to various technical, financial, environmental, political and social factors involved. Hallam Energy at Sheffield Hallam University was commissioned by the Government of India, to conduct a detailed independent investigation into the techno-economic feasibility of such a WTE project in Delhi. The goals of this study were (i) to make an informed decision on whether the proposed WTE facility for Delhi will be technically and financially viable, and (ii) to gain a reasonable understanding of the costs and resources involved in this investment. This work looks at the various challenges associated in setting up WTE plants in developing countries and address key findings including: 1. The capacity of the plant, 2. The capital cost, 3. The electrical power output, 4. Land area requirement, 5. Site selection for the plant, 6. The choice of processes and pre-processing of the feed, 7. Feasibility of trigeneration or CHP, 8. Choice of technologies and equipment, 9. Financial models, 10. Emissions of pollutants, 11. Lessons learnt from past WTE projects in India

Challenges in establishing waste-to-energy projects in developing countries with a case study from India

Municipal solid waste (MSW) management and its scientific disposal is a major concern for the local municipal authorities of all major Indian cities. Under the "Clean India Mission", the Ministry of Urban Development (MoUD) of India is investing US $9 Billion to clean up 75 largest cities in India. Waste to Energy (WTE) plants will be a key to its implementation. Currently, open air burning and landfilling are the most common practices of wase disposal in India. Landfilling is considered the least favourable option for cities as these sites occupy significant land areas in already crowded urban areas. WTE plants or incinerators are considered the most viable solution for safe disposal of MSW all over the world. In India, however, WTE projects have had mixed results and outright failures. Currently, only eight such plants are operational in the country. This is due to several technical, economic, environmental, social and policy factors involved. This study investigates the feasibility of a proposed state-of-the art WTE plant in Delhi which will set an example for other cities to follow. It reviews the various challenges involved in the implementation of such a project and suggests mitigating solutions to overcome these challenges

Experimental Validation of the Structural Integrity of Modular Horizontal Axis Wind Turbine Blades

The production, transportation and repair of long horizontal axis wind turbine blades measuring up to 85 m require expensive specialist machinery that increases the capital cost of wind power generation. A modular blade design is a potential solution to these problems however; the inclusion of joints could make the modular blades inherently weaker. This work investigates the effect of post-tensioned tendons on the structural integrity of modular blades, through cantilever deflection and tensile tests conducted on 3D printed small-scale prototypes. The experiment indicates 43% and 15.4% reduction in blade tip displacement and deflection caused by cyclic loading, respectively, in case of modular design with tendons compared to without tendons design

Achieving operational excellence for industrial baking ovens

A series of experiments were performed on industrial baking ovens across five confectionery manufacturing sites around the world. The impact of different operating parameters such as air and fuel flowrates, oven temperature, exhaust flowrates and ambient temperature etc., on the product quality and overall oven performance were investigated. The energy flows through the baking oven were modelled using experimentally determined inputs to estimate the reduction in heat losses. A step change in operational efficiency was achieved through the study delivering 8.5% improvement in the oven performance. On average, 92 tonnes/annum of CO2 were saved from each oven. An additional 7% efficiency improvement was observed by integrating the baking oven with a heat recovery technology saving circa £16k in fuel cost annually from a single oven. The observations and learnings from the work are not limited to baking ovens only, but can also be applied to other food manufacturing processes such as frying, broiling, roasting or grilling

Waste heat recovery from industrial baking ovens

Under this work, a system level energy model of an industrial-scale baking oven with an integrated waste heat recovery unit is developed using experimentally determined inputs to estimate the potential benefits of a gas-to-gas heat recovery system. This work has demonstrated that at least 4% savings in the oven fuel consumption can be achieved, reducing the annual running costs by £4,207. An environmental assessment indicates reduction of circa 43 tonnes in CO2 emissions per annum. The study also provides a systematic methodology to test low temperature gas-to-gas heat recovery technology for food manufacturing process

Techno-Economic Assessment of Waste Heat Recovery Technologies for the Food Processing Industry

The food manufacturing sector is one of the most dominant consumers of energy across the globe. Food processing methods such as drying, baking, frying, malting, roasting, etc. rely heavily on the heat released from burning fossil fuels, mainly natural gas or propane. Less than half of this heat contributes to the actual processing of the product and the remaining is released to the surroundings as waste heat, primarily through exhaust gases at 150 to 250 °C. Recovering this waste heat can deliver significant fuel, cost and CO2 savings. However, selecting an appropriate sink for this waste heat is challenging due to the relatively low source temperature. This study investigates a novel application of gas-to-air low temperature waste heat recovery technology for a confectionary manufacturing process, through a range of experiments. The recovered heat is used to preheat a baking oven’s combustion air at inlet before it enters the fuel-air mixture. The investigated technology is compared with other waste heat recovery schemes involving Regenerative Organic Rankine Cycles (RORC), Vapour Absorption Refrigeration (VAR) and hot water production. The findings indicate that utilising an oven’s exhaust gases to preheat combustion air can deliver up to 33% fuel savings, provided a sufficiently large heat sink in the form of oven combustion air is available. Due to a lower investment cost, the technology also offers a payback period of only 1.57 years, which makes it financially attractive when compared to others. The studied waste heat recovery technologies can deliver a CO2 savings of 28−356 tonnes per year from a single manufacturing site. The modelling and comparison methodology, observations and outcomes of this study can be extended to a variety of low temperature food manufacturing processes