Heat needs

The unit has virtually the same flow sheet (see Fig. 2) as that of methanol carbonylation to acetic acid (qv). Any water present in the methyl acetate feed is destroyed by recycle anhydride. Water impairs the catalyst. Carbonylation occurs in a sparged reactor, fitted with baffles to diminish entrainment of the catalyst-rich Hquid. Carbon monoxide is introduced at about 15—18 MPa from centrifugal, multistage compressors. Gaseous dimethyl ether from the reactor is recycled with the CO and occasional injections of methyl iodide and methyl acetate may be introduced. Near the end of the life of a catalyst charge, additional rhodium chloride, with or without a ligand, can be put into the system to increase anhydride production based on net noble metal introduced. The reaction is exothermic, thus no heat need be added and surplus heat can be recovered as low pressure steam. 

Thus the amount of heat that must be produced by burning coke ia the regenerator is set by the heat balance requirements and not directly set by the coke-making tendencies of the catalyst used ia the catalytic cracker or by the coking tendencies of the feed. Indirectly, these tendencies may cause the cracker operator to change some of the heat-balance elements, such as the amount of heat removed by a catalyst cooler or the amount put iato the system with the feed, which would then change the amount of heat needed from coke burning. 

Single-Effect Evaporators The heat requirements of a singleeffect continuous evaporator can be calculated by the usual methods of stoichiometry. If enthalpy data or specific heat and heat-of-solution data are not available, the heat requirement can be estimated as the sum of the heat needed to raise the feed from feed to product temperature and the heat required to evaporate the water. The latent heat of water is taken at the vapor-head pressure instead of at the product temperature in order to compensate partiaUv for any heat of solution. If sufficient vapor-pressure data are available for the solution, methods are available to calculate the true latent heat from the slope of the Diihriugliue [Othmer, Ind. Eng. Chem., 32, 841 (1940)]. 

In the first two types a brake shoe, operated by an external auxiliary supply, is mounted on the extended shaft at the NDE (non-driving end) of the motor. These brakes are normally operated after the motor is switched OFF. The heat of braking appears in the external circuit and the motor windings are not affected. For motors with this braking, only the starting heat need be considered, depending upon the frequency of starts and not the heat of braking. 

Extrusion blow moulding of bottles has been successfully accomplished in reeent years by attention to the points mentioned above. It is to be noted here that UP VC has a much lower average specific heat between the proeessing temperature and room temperature than polyethylene and, being essentially amorphous, no latent heat of fusion. This leads to much less heat needing to be removed on cooling of mouldings and very short cycle times are possible. 

Radiation is a process that is different from both conduction and convection, because the substances exchanging heat need not be touching and can even be separated by a vacuum. A law formulated by German physicist Max Planck in... 

A 0.6 gravity hydrocarbon gas flows from a 2-in. ID pipe through a I-in. ID orifice plate. The upstream temperature and pressure are 75°F and 800 psia, respectively. The downstream pressure is 200 psia. Does heating need to be applied to assure that frost does not clog the orifice What will be the flow rate ... 

Almost all heat loads fall into one of two categories. Either some material is to be heated from a lower temperature to a higher one or it is to be maintained at a high temperature while heat is supplied at a rate sufficient to balance the heat losses. In the first case the amount of heat needed to produce the change in temperature is given by... 

EXAMPLE 6.3 Calculating the heat needed to bring about a rise in temperature... 

A Z depends on the identity of the material. For instance, 50 J of heat increases the temperature of 1 mol of gold more than it increases the temperature of 1 mol of water. The dependence of AT on the identity of the material is expressed by the molar heat capacity (C, units J moP ° C ). The molar heat capacity is the amount of heat needed to raise the temperature of 1 mol of substance by 1 °C. Eveiy substance has a different value for C. The molar heat capacities of several chemical substances are listed in Table 6-1. 

The amount of heat required to vaporize a substance also depends on the size of the sample. Twice as much energy is required to vaporize two moles of water than one mole. The heat needed to vaporize one mole of a substance at its normal boiling point is called the molar heat of vaporization, A /fvap. 

Energy must also be provided to melt a solid substance. This energy is used to overcome the intermolecular forces that hold molecules or ions in fixed positions in the solid phase. Thus, the melting of a solid also has characteristic energy and enthalpy changes. The heat needed to melt one mole of a substance at its normal melting point is called the molar heat of fusion, Ai/fas... 

The amount of heat released by the complete combustion of one mole of a substance is defined as the heat of combustion, AAVcomb The amount of heat released may be measured in calories (cal) or in joules (J). A calorie is the amount of heat needed to raise the temperature of one gram of water one degree Celsius. The SI unit of heat is the joule. One joule is equal to 4.184 calories. 

In particular, the French were trying to use the steam from sugar boilers to heat sugar juice in a vacuum and evaporate the solution at low temperatures. A vacuum lowers the atmospheric pressure on the water s surface as a result, the water molecules can escape as steam at a lower temperature. The amount of latent heat needed to turn water into steam is nearly the same whether the water is in a vacuum or at atmospheric pressure. However, in the refining process, some heat escapes into the environment. Keeping water at a lower temperature reduces the amount of this lost heat and makes for a more efficient and potentially more profitable operation. 

Tubular reactors. Although tubular reactors often take the actual form of a tube, they can be any reactor in which there is steady movement only in one direction. If heat needs to be added or removed as the reaction proceeds, the tubes may be arranged in parallel, in a construction similar... 

In some situations, process heat needs to be supplied ... 

Some of the heat flows in Figure 16.18a are negative, which is infeasible. Heat cannot be transferred up the temperature scale. To make the cascade feasible, sufficient heat must be added from hot utility to make the heat flows to be at least zero. The smallest amount of heat needed from hot utility is the largest negative heat flow from Figure 16.18a, that is 7.5 MW. In Figure 16.18b, 7.5 MW is added from hot utility to the first interval. This does not change the heat balance within each interval, but increases... 

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