Energy balances and economics

1 Ethylene (ethene) and other olefins (alkenes). We will start with the simpler cracking of ethane according to the following equation and theoretical 

Ethane (M8 mol) Furnace fuel Steam consumed (net) Electricity 

Thus the net energy utilization is about 1 5 times the fuel value of ethylene, indicative of significant inefficiency in the overall process. (As an alternative to cracking. Union Carbide have patented improved catalysts for the selective oxidation of ethane to ethylene, which may ultimately prove more energetically and economically favourable.) 

The analysis of propane or naphtha cracking is rather more complex, owing to the variety of products formed, and changes in the distribution with operating conditions. However, some reasonably typical figures with ethane recycle (MJ/mol ethylene) are as follows  

From an economic viewpoint, the capital costs of naphtha-crackers are higher but naphtha is available worldwide whereas ethane availability is more limited, with the U.S. retaining a dominant, if no longer exclusive, position. 

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Anon. (1983), Assessment of the energy balances and economic consequences of the reduction and elimination of lead in gasoline . Working Group ERGA (Evolutions of Regulations, Global Approach). CONCAWE, La Haye. 

For those using this book as a text, I suggest that a specific process be chosen. Then, each week, one chapter should be read, and the principles applied to the specific process selected. The energy balance and economic chapters may each require two weeks. The pollution abatement chapter may be included after Chapter 8, or it can be studied as a separate topic unrelated to the over-all plant design. 

An analysis of the energy balance and economics of CO2 recycling to hydrocarbon fuels estimated that the full system can feasibly operate at 70% electridty-to-liquid fuel efficiency, and the price of electricity, needed to produce synthetic gasoline, is only 1.0-1.5% of the present sales price of gasoline. In regions where inexpensive renewable electricity is currently available, such as Iceland, fuel production may already be economical. The dominant costs of the process are the electricity cost and the capital cost of the electrochemical cell, where this capital cost is significantly increased, when operating intermittently (on renewable power sources such as solar and wind) [42]. 

For the student, this is a basic text for a first-level course in process engineering fluid mechanics, which emphasizes the systematic application of fundamental principles (e.g., macroscopic mass, energy, and momentum balances and economics) to the analysis of a variety of fluid problems of a practical nature. Methods of analysis of many of these operations have been taken from the recent technical literature, and have not previously been available in textbooks. This book includes numerous problems that illustrate these applications at the end of each chapter. 

The advances made in enzymatic hydrolysis of cellulosic materials (14) are also of interest. This technology involves only moderate temperature processes in simple equipment which promises to be of significantly lower capital cost than the pressure equipment associated with conventional acid wood hydrolysis processes. All of these considerations combined to lead us to study processes for ethanol production from wood, especially in an effort to obtain data for material and energy balances, and possibly for the economics. 

After writing mass balances, energy balances, and equilibrium relations, we need system property data to complete the formulation of the problem. Here, we divide the system property data into thermodynamic, transport, transfer, reaction properties, and economic data. Examples of thermodynamic properties are heat capacity, vapor pressure, and latent heat of vaporization. Transport properties include viscosity, thermal conductivity, and difiusivity. Corresponding to transport properties are the transfer coefficients, which are friction factor and heat and mass transfer coefficients. Chemical reaction properties are the reaction rate constant and activation energy. Finally, economic data are equipment costs, utility costs, inflation index, and other data, which were discussed in Chapter 2. 

Finally, to complete the formulation of the problem, we need system property data. For this particular problem, enthalpy, a thermodynamic property, is required for the energy balance and the overall heat-transfer coefficient, a transfer property, is needed for the rate equation. These system property relationships are given by Equations 4.4.8 to 4.4.10. The economic balance also requires cost data. 

A typical layout of a palm oil mill is shown in Figure 7 where the main stations of the process are also indicated. The equipment selected has to be carried out with care in order to obtain the correct balance for throughput, steam consumption, energy demands, and economics of the supply of stand-by equipment. Standardization of equipment is an important point to consider when selecting machinery on the basis of within mill and between mills when applicable. When a set range and/or make of equipment can be chosen (e.g., valves, gearboxes, electric motors and starts, etc.), considerable benefits can accrue by way of a reduction in the amount of spare parts to be carried. 

Recently, Agrawal et al. (2006) had modeled the LDPE reactor as an ideal plug flow reactor and presented all the model equations and parameters for use by researchers. The model equations include ordinary differential equations for overall and component mass balances, energy balance and momentum balance. The reactor model of Agrawal et al. (2006) is adopted, and cost expressions and economic objectives are... 

To allow a preliminary mass and energy balance and hence to show up useful waste heat which might be used elsewhere in the process, identify byproducts which might be sold and improve the process economics, etc ... 

H. L. MuUer and S. P. Ho, "Economics and Energy Balance of Ethanol as Motor Fuel," paper presented at 1986 SpringAIChE Mational Meeting, New Orleans, La., Apr. 1986. 

Adsorption The design of gas-adsorption equipment is in many ways analogous to the design of gas-absorption equipment, with a solid adsorbent replacing the liqiiid solvent (see Secs. 16 and 19). Similarity is evident in the material- and energy-balance equations as well as in the methods employed to determine the column height. The final choice, as one would expect, rests with the overall process economics. 

Implementation of P2 (pollution prevention) measures can yield both economic and environmental benefits. However, a balance on energy usage and environmental impacts may have to be struck. New refineries should be designed to maximize energy conservation and reduce hydrocarbon losses. 

Economics. Comparison of the material and energy balance for our process and the cobalt-based BASF higher olefin process (8), we foimd that our process reduced the capital investment required by over 50% due to the fact that we require far fewer unit operations, and because the operating pressure is much lower. In sutmnary, the thermomorphic solution developed by TDA allows easy catalyst recycle, which, when coupled with the lower pressure operation possible with Rh catalysts (compared to the cobalt-based process) lowers both capital and operating costs for current oxidation (oxo) plants of similar capacity. 

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