Topic: Flue Gas as Heat Recovery
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Quantity of Heat from Flue Gas
The quantity of recoverable heat from the flue gas is actually recovered from gases like carbon dioxide, steam and oxygen. Since the figure of these gases is 26.18 percent, thus this working will be based on this amount from the flow rate of 39000m3h.
From the ideal gas formula below;
PV = RTP =RT/VIf P – which is pressure can be equated to the work donei.e. W- will be denoted the work done. From the principal of conservation of energy, we can assume that the work done will be proportional to the amount of energy liberated. Then w=rt which can then be shown as R(T-T*)P- Pressure,R –is a constant called the molar gas constantT- is temperature of the flue gas.Therefore the actual recoverable heat energy will be calculated from 26.18% of the 39000m3h of gas flow. 26,18 x39000m3/100=10210.2m3h of gas .Then from the ideal gas equation will beW= R(T-T*), Where the T, and T* represent the temperature change is T and is found by subtracting 200 from 350 ( 350 -200) for Temperature change.If at atmospheric conditions P= 76m of mercury;Then from PV= RT10210,2 x76m =R(150)775975.2 =R(150)775975.2/150 =R51731.68 = RWhere R – is the molar constant and is to be given as 1.013x105nm-2kTherefore; 1.013 x105nm-2k x150 equals 1.5195x108nm-2k=151950000/775975.2=19.5753729 per hour
In 24 hours. = 19.5753729x 24= 469.80895kwh
Electricity Generation from Waste HeatThermal Electricity Generation: In the thermal generation of electricity, the flue gas can be used to heat boiler steam converting the boiler steam into steam energy which will then be converted by turbines to generate electricity. Electricity is generated by the rotating action of the turbines which will turn a generator i.e. dynamo. The turning effect of the generator will produce electricity. For enhanced efficiency of the boiler the steam turbine performance can be improved by refurbishing. This will include removal of deposits that can cause reduction in blade aero dynamic performance, adjusting shaft and blade seals (Ganapathy, Victor, 2002, p78).
The newer the blades used in this section the efficiency and effective the work output as compared to the older one. This applies to all the parts used in the whole section of the turbine. This will be used as one way of improving efficiency of all parts thus it will have greatly increased the boiler’s performance, by increasing the steam turbine efficiency. This system is cost-effective as the electricity generated in the factory can act as substitute power to the costly electricity that could be offered by private agencies and other governmental organizations. This can generate more profits to the company since the expenses incurred in energy costs could be reduced and thus, enhance the maximization of the organizational value and profits in the long run.
Rankine Cycle Electricity Generation
This system is a newer invention that is basically used by Ener-G-Rotor Company in generating electricity from waste gases at lower temperatures. It is an imperative procedure of cost-effectively generating electricity from low-temperature waste heat. The system uses a rotor instead of a turbine to run the generator. The system is based on the Rakine Cycle where heated fluid that passes through a tube heats up a pressurized fluid in a second tube through a heat exchanger. The fluid vaporizes and travels into a large space called an expander where it exerts a mechanical force that can be converted into electricity.
This Rankine cycle system can be adopted by this glass manufacturing company in South Yorkshire so as to cut on electricity costs. It ought to be understood that the rotor design is simpler than that of the turbine as indicated in the preceding thermal method of heat generation from waste gases (Wood, Jack, 2008, p47). Given that this method is potentially easier to use, it is also cheaper to manufacture electricity alongside being more durable. Another significance of this system is its ability to generate electricity from gases at lower temperatures than when turbines are used, which need higher temperatures and energy consumption.
Cooling the Bottles Once they are out of the Furnace
Annealing is a commonly used method of slowly cooling glass in an annealer to release any stress and strain that could have been created during the formation and molding of the glass bottles in this context (Doty & Turner, 2009, p118). Proper annealing is pivotal and critical in glass making as glass that is allowed to cool quickly will break as it cools or could be highly strained when it reaches room temperature and is prone to easily break due to a high level of brittleness. This section of paper will offer some information on methods of glass cooling;
Crash Cooling
This method involves opening the kiln to cool faster from the processing temperature to the annealing temperature and this is done to avoid devit from forming on the glass. This method is faster in cooling the glass as well as in slumping glass through a drop ring (NKK Technical, 2011, p 268). Despite this, there are limitations of using this method as it is limited to kilns with kilns that have fiber glass in nature. This means that it will be difficult to conduct crash cooling of glass on the fire bricks and elements inside the kiln. It also results in wear, aggravation and stress on the kiln leading to cracking and falling of particles onto items that could have already been manufactured resulting into losses.
Closing/ putting off the Furnace
Apart from crash or rapid cooling of the glass in the manufacturing firm, the operators can put off or close the furnace so as to allow the glass to cool. However, this method has limitations in cases where there are a series of operations to be conducted by the company. It is also not suitable where the furnace walls are made of fiber glass and therefore the crash cooling process would be preferred (Wang Zhao-Wen, 2008, p.77). Despite this, it is a cost-effective method since the waste heat can be diverted to other parts of the system in the generation of electricity or pre-heating of the feedstock before melting in the furnace as indicated in the succeeding parts of the paper. This is also a pivotal method and should be considered in the glass cooling segment of processing.
Pre-heating the Feedstock before melting it in the Furnace
The waste heat can be used in pre-heating the feedstock before melting it in the furnace. This means that the heat is not only used in the generation of electricity and cooling of the molded glass but also in softening the raw materials used in the manufacture of glass. This is an imperative step in the glass manufacturing process as it reduces waste of resources (heat) while maximizing the effectiveness in the operations of the industry (Doty & Turner, 2009, p97). This process is vital as it will ensure that the company adheres to the occupational health and safety legislative policies that are set up in South Yorkshire. The litigation charges and penalties resulting from nitrogenous and sulphate gas emissions will be reduced and thus, ensure that the company operates within the environmentally friendly codes of conduct.
This will not only be beneficial to the company in terms of its economic and financial or legal needs but will also enhance the corporate image of the company as it continues recycling glass. This is attributed to the fact that the waste gas could be used in generation of power to smolder the glass pieces and convert them to feedstock before being transferred to the finishing and cooling chambers so as to produce different shapes of glass bottles (Ganapathy, Victor, 2002, p. 85). Essentially, maximizing on the usage of waste gases and heat generation in the firm will have long turn benevolent effects to the company from multifaceted aspects such as increased profitability, reduced legal charges (resulting from environmental pollution) and the enhancement of the organizations corporate image.
Savings, Payback Period and Capital Investments Needed from the Technology Options
In order to present information that could be reasonable in the adoption of the technologies identified in usage of waste heat and making maximum usage of the gases, the following assumptions ought to be put in consideration:
The current prices of gas and electricity (excluding VAT) remain unchanged at Gas: 3.2 p/kWh and Electricity: 8.7 p/kWh throughout the year.
The factory’s capacity remains constant at 97,000 tons of glass per year
The annual gas and electricity bills remain unchanged at 4,000,000 pounds and 85,000 pounds annually respectively.
The cost consumption of the three categories in which waste heat is prioritized is the same during and throughout the entire operational life of the company.
Based on these underlying assumptions, the costs or capital investments needed in each of the technologies in the priority areas will be given as follows:
Given that PV= RT10210,2 x76m =R(150)775975.2 =R(150)775975.2/150 =R51731.68 = RWhere R – is the molar constant and is to be given as 1.013x105nm-2kTherefore; 1.013 x105nm-2k x150 equals 1.5195x108nm-2k=151950000/775975.2=19.5753729 per hour
469.80895kwh/day
Multiplying this by 3.2 x 365 (cost and number of days), gives;
469.8089 = 548, 736.7952 (for Gas bills)
469.8089 x 365 x 8.7 = 1, 491, 878.16 (for electricity bills)
The total cost will be 2,040,614.95 pounds.
This means that the savings on an annual basis will be given as follows;
[4,000,000 + 85,000] – [2,040,614.95]
Thus, savings will be 4,085,000 -2,040,614.95 = 2,044,385.05 pounds
The computations in this case are done based on an annual basis and the prices per kilowatt are assumed to be constant over the year, the payback period would be estimated to be a year. Given that waste heat is to be incorporated in three different processes within the manufacture of glass at the factory, it is estimated that the costs could be met within a year for each of the technologies used, based on the cost of electricity and gases that would be used in the cooling processes, thermal generation of electricity and the conversion of the glass particles to feedstock (Doty & Turner, 2009, p123).
Therefore, the costs to be incurred in capital investment would be as follows;
2,040,614.95 x 3 (the departments) = 6,121,844.85 this is based on the assumption that the three activities within which waste heat is used have equal capital consumption. It is from this assumption and computation that the total payback period for this investment is determined at a period of 3 years.
Conclusion and Recommendations
An analysis of the operations of the company and its intended goals of making use of waste heat seems to be of great benevolence to the company in the long run. These assertions are based on the facts that costs of production or manufacture of glass will be reduced. There are multifaceted benefits that will accrue to the organization ranging from financial, legal and social aspects. For instance, the profits will be increased; the company’s corporate image will be enhanced for taking care of the environment and using environmentally friendly resources. Legal aspects of the company will be free of litigations and penalties and thus, would attract more investors who will in turn facilitate positive results (Ganapathy, Victor, 2002, p103).
The company will therefore perform better than others in the industry due to its effective and efficient operations in the long run. It is vital that the company adopts the postulated technical activities in making use of the waste heat in the generation of electricity, cooling of glass and preheating the glass particles to convert them into feedstock before moving them into the furnace (NKK Technical, 2011, p 265). It is also vital to understand that the payback period is small period which will create immense benefits to the company in terms of its efficacy in operations through reduction of costs and expansion of its profits yield.
References:
NKK Technical, 2011, Biomass Power Generation by CFB Boiler, Koji Yamamoto, NKK Technical Press.
Wang Zhao-Wen, 2008, Molecular Mechanisms of Neurotransmitter Release, Contemporary Neuroscience, WangSpringer.
Doty, Steve & Turner, Wayne, C, 2009, Energy management handbook, Edition7, New York, The Fairmont Press, Inc.
Ganapathy, Victor, 2002, Industrial Boilers and Heat Recovery Steam Generators: Design, Applications and Calculations, Volume 149 of Mechanical engineering, California, CRC Press
Wood, Jack, 2008, Continuous Electrodeionization for Power Plant Applications”, Filtration+Separation, New York, University Oxford of Press.
