Document 85yRnqgO0JDqBO2bqrYxo65me

770 CHAPTER 71 1962 Guide And Data Book the jacket can be t-a-kpn directly into a suction line leading to the compressors, fig. 9 illustrates this type of jacket cool ing. For the method using the hand valve and solenoid valve, the branch suction line should enter the suction main ahead of a suction trap or a low-pressure receiver. For rotary low-stage compressors, it is desirable to main tain even temperatures around the cylinder in order to obtain even expansion and contraction and one method of accom plishing this is to flood the cooling chamber with a fluid such as Refrigerant 11 and let this fluid operate in a thermal cycle, fig. 10 shows an arrangement with this type of cooling. Re frigerant 11 flows as a liquid from the upper chamber into the annnlftr space of the rotary compressor, where some of it evaporates and flows out the top connection of the rotary compressor back into the upper shell where it is condensed by circulating cooling water. Among other methods that have been used for cooling rotary compressors are water or oil circulation through the annnlftr space. CONDENSER AND RECOVER PIPING The main consideration in the piping around condensers and receivers is to keep the condensing surface at its highest efficiency. To do this, it is necessary to keep the liquid am monia draining out of the condenser promptly as it is con densed and also to keep air and other non-condensables purged out. Horizontal Condenser and Through Receiver fig. 11 shows a horizontal water-cooled condenser draining into a through type receiver. Water is introduced into the lower tubes of the condenser and leaves from the upper tube* This method results in the highest log mean temperature difference and will keep the condensing pressure at the low^ value. Since air is heavier than ammonia vapor, it will tend to migrate to the lower part of the shell where the water k coldest. Control of water flow to maintain head pressure is not al ways necessary in ammonia plants. There b usually ade quate pressure to force the ammonia to the various evapora tors without water regulation. The economics of each situa tion has to be evaluated on the basis of water costs versus brake horsepower cost savings at lower head pressures. The water piping should be arranged to keep the condenser tubes filled .with water at all times. Air vents should be pro vided on the condenser heads with hand valves for m*n11n] purging. Receivers should always be located below the condenser so that the condensing surface b not flooded with ftmmnn^ The piping should be such that there b free drainage aw&y fron the condenser and that the static height of nmmonin above the first valve out of the condenser b greater tliAn the pressure drop through the valve. The drain line from .the condenser to receiver b cn the basis of 100 fpm maximum velocity in order to allow gas equalization between condenser and receiver, and also allow the air to migrate into the receiver. Sizing of thb liTM_ based on pounds of ammonia per minute b given in Table 1. Any ammonia vessel that can be valved off must be pro vided with an automatic relief valve. Sizing of the valve should be in accordance with National Board of Boiler mid Pressure Vessel Inspectors. The valve should be automatic reseating. In order to be able to test relief valves, it b necessary to be able to pump out the vessel or provide a maaTM of tmg a dual valve, such as* b shown in fig. 12, using two relief valves. The stop valve b constructed so that it b always open to one of the relief valves while the other b being removed for checking. Refrigerant Piping Systems for Ammonia 771 A dual type relief valve b recommended for use on receivers kyjinsMk normally it b not possible to put all the liquid am* juojaa in the low side. On condensers and other system compocents that can be pumped out easily, a single relief valve _m_av be used. A non-condensable gas separator (purge unit) b useful on oKtst plants but especially where a suction pressure below 0 r&z is used. Purge units on ftmmnnift systems are piped to the receiver as shown in Fig. 13. High-pressure liquid b ex ploded through a coil in the purge unit, providing a cold gpot in the purge drum. The suction from the coil should be tofroti into one of the high-temperature suction mains. Amjprtnift vapor and non-condensable gas are drawn up into the purge drum and the ammonia b condensed on the cold surface and drained back to the receiver. When the drum fills up with air other non-condensables, the thermostatic valve opens permitting them to leave the drum and pass into the open bottle. When the non-condensables leave, the bulb on the thermostatic valve warms up to close the valve. A receiver should be equipped with a gage glass so that ffie quantity of ourmnnift in the receiver can be easily deter mined. The valves on each side of the gage glass should be constructed with a check valve in such a way that if the glass breaks, the check valve will prevent loss of the refrig erant from the receiver. Fig. 14 illustrates a gage glass as sembly. ftnffinipnt liquid ammonia has to be charged into the system to s&l the outlet pipe of the receiver and to prevent hot gas horn blowing over to the low side. The outlet pipe should extend down into the receiver to a distance of one pipe di ameter from the bottom. The lowest liquid level in the re ceiver should be equivalent to two diameters of the outlet pipe for both top ami bottom outlet receivers. For a iyi in. top outlet on a 30 in. diameter receiver, the pip* should extend to 1% in. of the bottom of .the receiver and the lowest ammonia level should be 2^ in. from the bot tom of the receiver. A through type receiver b piped so that all of the ammonia from the condenser passes through on the way to the low tide. It should be large enough to at least take care of the fluctuation in liquid supply to the low side. It b helpful for mainiAnanop if it b sized to hold tiie entire plant charge. Parallel Condensers Two condensers operating in parallel with one through type receiver are shown in Fig. 15. The length of horizontal liquid drain linea to the receiver should be kept to a minimum. Equalization between the shells b accomplished by keeping the velocity in the1drain line within 100 fpm. The drain line may be tized from Table 1 or from Chapter 69. Fig. 10.... Rotary Booster Compressor Coding with Refrigerant 11 Thermocyde fig. II .... Horizontal Condenser and Through Receiver Piping Fig. 12 .... Dual Relief Valve Fitting for Ammonia Condenser fig. 14