CASE HISTORY
COMPRESSOR STATION NOISE CONTROL ON TURN KEY BASIS
BOKARO STEEL PLANT

PROJECT:

M/S. Bokaro steel plant is having a central compressor plant, which houses 5 Nos. of compressors to feed the utility air for the entire steel plant. These compressors are emitting a very high noise level of 110 to 114 dBA. The compressors are installed at an elevated level. The intercoolers, after coolers, moisture separator etc., are installed right below the compressor on the ground.The compressor gearbox, the intercooler, after cooler, moisture separator, lubricating system, by pass piping, pressure throttling are the basic sources of noise.

As the control room is located near to these compressors a very high noise level was observed in the control room area and thereby creating occupational hazards not only to the person working in the control room but also to the maintenance gang working in the compressor plant. The management of the Bokaro steel plant decided to implement a noise control system on turn - key basis to protect the operators working in these plants and those others affected due to high noise exposure .The contract on turn-key basis to bring down the noise level within the acceptable limit was awarded to M/S. Acoustics India Private Limited who is the pioneer in the field of noise pollution control services in the country.

Fig.1
View of 4 Nos. Compressor Enclosure

NOISE SURVEY:

M/S. AIPL carried out a very detailed noise survey, identified the critical areas and recorded the following noise level

Freq(Hz) 63 126 250 500 1K 2K 4K 8K
SPL dBA 103 110 111 103 103 110 102 95


Fig.2: Inside View Of Compressor Enclosure
NOISE EMITTING SOURCES:

After a thorough analysis of the survey report, it was observed that the following components are predominantly emitting a very high noise level

  Compressor casing

  Gear box

  Lubrication system

  Suction ducting

  Discharge ducting

  Noise emitted from intercooler, after cooler, moisture separator

  Noise transmission through suction ducting, discharge ducting and valve throttling

  other structure borne noise

NOISE CRITERION:

M/S. Bokaro steel plant desired to bring down the noise level within 85 dBA at a distance of 1 meter from the enclosure anywhere inside compressor building. As these compressors are of Russian make and designed for certain temperature conditions to protect the health of the equipment, M/s. Bokaro Steel Plant desired to restrict the temperature raise inside the acoustic enclosure within 3 degree centigrade above ambient temperature. The design was based to meet this criterion.
SOLUTION

        Detailed design analysis was carried out to arrive at a solution so that noise emission from various sources is restricted within guaranteed level. A scheme in the form of drawings was prepared for the total noise control. While designing noise control systems one of the basic requirements is to take care of the operator's requirement from the point of maintenance. After detailed discussions with engineers from user department, design department, maintenance department of steel plant a final scheme was arrived at and the required components were manufactured.


        The suction noise was reduced by installing a splitter banks on the suction chamber and part of the suction ducting was acoustically insulated.
        The discharge noise was restricted by installing a discharge silencer which is a pressure part with stainless steel internals construction to restrict the fluid borne noise transmission at the outlet of the silencer within the specified limit.
        The compressor and gearbox were enclosed using collapsible type acoustic enclosure with adequate provision for maintenance.

Fig.3
View of compressor enclosure from motor side
         The acoustic enclosure was also provided with a sound proof industrial sound reducing doors so that the routine checkup or minor maintenance could be carried out by the operator by getting into the acoustic enclosure through the sound reducing doors as sufficient space inside the enclosure is provided around the compressor for an operator to move around on all sides. The acoustic enclosure was suitably illuminated and the ventilation arrangement with ventilation silencers and ventilation Blowers were provided to restrict the temperature raise within 3 degree centigrade above the ambient temperature.
        The intercooler and after cooler were also acoustically enclosed with suitable ventilation arrangement so that the temperature raise on the skin surface do not affect the performance of the equipment. All the structure borne noise transmission path were traced and acoustically treated to maintain the noise level within the desired limit.
        The system also involves a motor control center at a centralized location to control the complete electrical requirements of ventilation fans, lighting arrangements.

CONCLUSION:

          After completing the erection of total system, a noise survey was conducted jointly by AIPL and the environmental engineering department of BSP. The noise level was observed to be well within 84 dBA when measured anywhere inside the compressor plant .The temperature raise due to acoustic enclosure when measured inside the acoustic enclosure was found to be within 3 degree centigrade above ambient temperature.


Fig.4
View of coolers and compressor acoustic enclosure
  It is not possible to cover all the complexities of this major noise control project in a brief article, but hopefully it does give some concept of the scale and degree of technical expertise for both engineering and noise control technology which is demanded and of the difficulties involved. In all, completion of the project took around 9 months and demanded close liaison between acoustic engineers, project engineers, structural specialists, civil engineers, electrical and ventilation experts.
  
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