In order to drain toxic or hazardous media, it is essential to achieve a clean separation of the phases. If gases in this class have to be drained to protect plant components and ensure the safety of the process, plant operators are often faced with a problem. By using a steam trap with gas-tight, under-level, rotary slide valve control, the liquid can be discharged both reliably and safely.
As a manufacturer of special valves, Rifox is a problem solver for unusual challenges involving condensate and drainage. The company places its trust in the proven rotary slide valve control and, to meet extra requirements such as gas-tightness for reasons of safety and the environment, its own development work: the gas-tight, under-level version of this technology. The rotary slide valve control has the functional characteristic of a proportional controller; the condensate flow rate depends on the actual amount of condensate, i.e. the condensate level in the body, and the pressure difference at the closing system. One good example of an application for the rotary slide valve control is the drainage of furnace gas, a waste product arising in the production of steel in blast furnaces. This gas mixture consists of about 50 % nitrogen, 25 % carbon monoxide, 22 % carbon dioxide and 3 % hydrogen.
The high proportion of the toxic and combustible CO represents both a hazard and a significant potential benefit, because its calorific value is 3.5 MJ/m³. Furnace gas is extracted in the hot state at the top end of the blast furnace, and then purified in a furnace gas scrubber. After this, the furnace gas is conveyed in large-diameter pipes, sometimes over long distances, to other applications. During transport, the cooling process generates enormous quantities of condensate, which must subsequently be removed from the system in a reliable manner. The problem here lies in the varying degree to which the gas is polluted by dust particles and other contaminants. It is important to ensure discharge of up to 20 t/h of condensate at a pressure differential of up to 4 bar without any banking-up. The steam trap is generally located outdoors and must also provide reliable service at sub-zero temperatures. What’s more, it must be gas-tight in normal operation, since the condensates are discharged into open collecting basins.
With gas-tight, under-level control
The task of draining the furnace gas was solved with the aid of the Rifomat EF-1018 PN 16 (size 100), which offers gas-tight, under-level control. With its generous dimensions and angle-pattern body, this steam trap has all the features needed for the challenge. Its low sensitivity to dirt load results from the operating principle of the rotary slide valve control; this capability is further enhanced by the large opening cross-section of 16.5 cm², which makes blockages almost impossible.
There is a flushing connection at the side as well as a drain plug underneath the trap to enable dirt to be purged for maintenance purposes. When there is a danger of frost, the unit’s functional reliability is safeguarded by a double bottom, as a heating pocket that covers the entire base of the body. This pocket can be heated by steam, thermal oil or pressurised hot water.
Insensitive to dirt
The gas-tight, under-level float control used in the above example has a metallic valve seat. Complete gas-tightness can only be achieved in the gas-tight, under-level version if the rotary slide (as the closing system) always lies below the condensate level in both the open and the closed position. This condition is met in the design by the adjustment of the angle between the rotary slide and the float. The condensate above the rotary slide effectively shuts off the gas. The permanent presence of the minimum water level is therefore a precondition of complete gas-tightness.
The robustness of this steam trap against dirt particles is also advantageous in many other applications. The condensate is discharged reliably through the large cross-section of the rotary slide. As there is only one moving part, the valve boasts a very long service life. The edge of the rotary slide does not function as a sealing lip. On the contrary, it pushes dirt particles from the seat with every movement, keeping it free of fouling. The sealing action is performed by the overlapping surfaces of the supporting structure and the rotary slide. Even after several years of operation, the closing system shows no signs of deteriorating but retains virtually the same high level of shut-off over the entire life cycle of the control.
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For over 60 years now, Rifox has been an innovative manufacturer of valves for steam, compressed air and condensate. On 11 February 1949, Hans E. Richter founded the company Rifox-Hans Richter GmbH in Bremen, and his Hanseatic motto of “Abroad and at home, venture and win” led to enduring success. Superior engineering and high precision, coupled with the greatest possible simplicity, proved to be the winning formula for this inventive entrepreneur. Today, this approach is still used for ensuring reliability and durability when applying the latest technologies. As a competent partner for companies in the chemical, petrochemical, foodstuff and medical product sectors, Rifox has secured itself a firm place in the industry with solutions that ideally meet the needs of all users of steam technology. The certification to DIN EN ISO 9001:2000 as well as the design and classification of the firm’s products in accordance with the Pressure Equipment Directive 97/23/EC for the first time in 2001 are guarantees of constantly high standards. New applications always call for innovative implementation. For custom implementations and individual designs in particular, Rifox is a trusted adviser. Tailored solutions are worked out in close dialogue with the customer.
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