Energy Conservation Consultants, Thermal & Electrical Energy Audit, Water Audit, Safety Audit, Project Management Service, Energy Management Services.

Case Study.......

INTRODUCTION : Boiler is the most commonly found energy equipment in the industry.   Performance of the boiler system not only affects the fuel consumption directly, but also, at times controls the production output and quality of product. The Steam system comprises of following components:

• Non – IBR (or coil type boilers)
• Package (or smoke tube IBR boilers)
• Large water tube boilers

Though the classification is based on the IBR regulations, it has a greater significance from energy conservation angle. The energy conservation opportunities associated with each of the above boilers are different, so are the problems faced by the end users.

We have incorporated the case studies classifying them under the above headings. The facts and figures are from actual field study measurement whereas names of the company are not mentioned to maintain secrecy.

STEAM GENERATION SYSTEM :

The first and foremost activity to be conducted in the energy management program is to evaluate the boiler efficiency. Format for collecting data for boiler efficiency is enclosed as Appendix I and the Work sheet for evaluating boiler efficiency from the collected Data. Fortunately the efficiency evaluation procedure for all the boilers is same regardless of its classification.

Following is the boiler efficiency test conducted on a non-IBR boiler.

BOILER EFFICIENCY EVALUATION CALCULATIONS (850 kg/hr)

Ultimate Analysis of fuel (w/w):

Indirect Efficiency Test

Comments: Though the boiler efficiency of 84% by indirect method shows that the performance of boiler is very good.   However, due to the design of non-IBR boilers, there is lot of heat wastage from water carry over and wet steam.  This is normally not accounted in the plant efficiency evaluations.  The contribution of economiser diminishes as the feed water temperature increases due to condensate recovery.  That is the reason why Useful heat to process is as low as 72.90% against the Indirect boiler efficiency of 84.40%  

Tuning of boiler Boiler efficiency test for both the boilers was carried out during the Energy Audit study. Major findings  of the test before are as follows:

Boiler Tuning: During he Energy Audit study, boiler tuning was done, 
the tuning of boiler has led to following results:

This tuning of boiler is expected to reduce the fuel bill by around 5 to 10% depending upon the operating hours of the boilers. This tuning is done by reducing the fuel quantity and optimizing the air to fuel ratio. Normally, the plant operators change the settings arbitrarily. It is, therefore, necessary to do this exercise periodically.

The minimum monetary saving expected is Rs. 1.5 Lacs per annum.

WASTE HEAT RECOVERY FROM THERMOPAC STACK :

The Thermic fluid heater burner has a capacity of 1 Lac kCal/hr (corresponding to 10 kg/hr LPG firing.). Flue gas temperature is 300°C & flow rate is 302 M3/hr.

It is therefore proposed to tap heat content in flue gases by installing Waste Heat Steam Generator in the stack.

Steam qty.(@3 kg/cm2 ) that can be generated through the available 
Waste Heat

Comments: Though the Thermopac capacity and quantity of steam generated are very small, the payback period is very attractive. The same logic can be extrapolated to any size of Waste Heat Recovery system.

STEAM DISTRIBUTION SYSTEM:

The steam distribution system comprises of the following components:

1. Moisture separator
2. Pressure reducing station
3. Piping and its insulation
4. Steam traps  

Following are some of the hard facts regarding steam losses in various components of Steam Distribution system.

Leakage:

Loss Due To Improper Insulation

Relation of steam velocities and pressure drop in the pipe :

How to read the above table : Example: For 6” pipe, at 7 kg/cm2 pressure the pressure drop in the pipe shall be:

Case Study to elaborate the effect of insulation of flanges: 
100 ft of 6 Inch pipe 12 Flanges of 6 Inch = 5 ft of pipe length Heat loss 
in following 3 cases :

Case (I) – Bare pipe ( Bare Flanges) 
Case (II) – Pipe with 2 inch insulation aluminum cladding and bare flanges 
Case (III) – Insulated pipe and Flanges

Present Scenario

No moisture separator installed in the line and only TD traps for drain points 
After the Moisture separator was installed in the pipeline:

Energy Conservation Potential :

Additionally the production capacity increased due to availability 
of the production equipment for longer durations.

STEAM UTILIZATION SYSTEM : This area is most potent for energy conservation.  The application, end use utility and quality of steam are the three main points that govern energy performance of the system. Energy performance of the system can be drastically improved by close examination of the system. The energy saving is affected by following measures:

Reducing the demand of steam by modification of application system by:

• Reduction in operating hours

• Reduction in quantity required per hour

• Use of more efficient technology

• Minimizing wastage

We shall elaborate the efficiency enhancement process by suitable 
examples of each type.

CASE I:    Reduction in demand of steam in belt dryer system

System Description and present operating conditions

A belt dryer in one of the chemical industries is using steam for heating the drying air. The energy inputs to the system are:

Initial performance parameters were established by field measurements 
and the performance was monitored for few batches. 
Following is summary of performance parameters at present conditions :

Recommendation :

Start the circulating fans in each section and cut down the blower flow rate. Replace the blower with smaller size blower.

Following is summary of performance parameters at proposed conditions:

Energy savings :

The energy consumption of proposed system shall be:

• Steam for air heating : 90kg/hr

• Electrical energy for FD : 2 kW

• Electrical energy for FD

Comments : This is a typical example where reduction in demand by modification in the end application leads to a mammoth saving of 75%.

CASE II:    Reduction in steam demand by use of hot water in the process:

System description : Cold water is taken to the reactor and then heated to desired temperature. The average time taken for getting the desired temperature is between 1 to 2 hours. This instantaneous heat load leads to pressure drop in the boiler. Once the temperature is attended, the steam requirement is hardly anything. The hot water is then drained to ETP as there is no condensate recovery system.

Recommendation :  Hot water shall be used for the process the loss due to condensate draining is eliminated completely, and the average batch time shall reduce by 1.5 hrs.

Using the heat available in the boiler economiser can generate the hot water required for process. This shall also ensure that there is no loss of heat through the feed water tank.

It is required to increase the capacity of the tank to 10 KL and insulate the tanks. If hot water at a desired temperature is required, one steam blower can be installed that shall mix live steam with water instead of indirect heating.

Saving potential : Investment required for implementation of all the modifications shall be in the range of Rs. 45,000/-   The energy saving potential is Rs. 1,00,000/- per year

Comments :  The savings achieved in this case are due to reduction in operating hours of steam requirement and Waste Heat Recovery. It must be noted that there is a productivity improvement as the batch time is reduced by 1.5 hours.

CASE III: Reduction in steam demand by use of Multiple Effect Evaporators :

System description :  The plant has a single effect evaporator to concentrate 250 m3/day of a stream from 15% concentration to solid.   The system parameters are :

Recommendation and saving potentials:

There is a possibility of installing 4-effect or 6-effect or 12-effect evaporator system. The saving potentials and the investments in all the three systems is as follows :

Comments:    This is a typical case of reduction in steam demand by use of more efficient technology. Here the investment is also proportionately high, but in the larger perspective, it pays to switch to a more efficient technology.

CASE IV:  Reduction in wastage of steam by use of thermocompressor System description :

Thermocompressors are heat pumps, where low level (low-pressure) steam is compressed by using motive steam at high pressure. In the process of compression, vacuum is also generated in the connected equipment. For evaporator applications the vapour generated in the body is compressed using thermocompressors and the discharge steam is passed to the calendria. Live steam, which was earlier fed to the calendria, shall now pass through the Thermocompressor at a higher pressure. Steam generation at higher pressure also helps improving efficiency of boiler operation.

The savings shall occur on the following accounts :

• Reduced steam consumption

• Elimination of Vacuum pump operation

• Proportionate reduction in the cooling water circulation

• Improved boiler efficiency on account of steam 
  generation at higher pressure

The following analysis shall quantify effect of each of the parameters on energy saving.

APPENDIX I : INDIRECT BOILER EFFICIENCY TEST OBSERVATIONS 
(850 kg/hr boiler)

Observation table :

Designed & Hosted by : MID   Promoted by : GID