8 Reasons Why Some Green Roofs Are White

The city of Chicago has been setting up what it calls “green roofs,” which is literally covering city rooftops in vegetation. While this may be a great idea for some buildings, it’s just not practical for all situations. How do you do maintenance on a building topped with greenery? It’s not nearly as simple as doing maintenance on one that is sans verdure.

However, a building surface that is both environmentally friendly and easy to care for is a cool roof. This option is both reflective and emissive, and it is specifically designed to be eco-friendly without creating an ecosystem on the roof itself.

Below are some specifications for this type of environmentally-friendly option:

• A green roofing system will help keep those under it cool on a hot summer’s day.

• It is made of vinyl and feather light, while traditional options can be quite heavy.

• It can house solar panels—or, if you so choose, even rooftop vegetation.

• They use green roofing materials that are 100% recyclable. There is minimal waste created from its setup, and the waste that is created is recycled back into building materials. At the end of the rooftop’s life, the whole thing can be recycled.

• Eco-roofs have a longer life than traditional ones. Since a large portion of the damage done comes from heat absorption, and cool roofs absorb less heat, this building surface option will live long and prosper. With the appropriate maintenance (which really is just infrequent cleaning), it will last much, much longer than a traditional choice.

• They have ENERGY STAR labels. This means that they are designated as a product that uses an amount of energy that is 20-30% below federal standards.

• A sustainable rooftop will help a building earn a favorable Green Globe rating and a favorable Leadership in Energy and Environmental Design (LEED) rating. These ratings can translate directly into more business for you and your company.

To be environmentally friendly, the top of your building does not actually have to turn the color green. Many of these surfaces are actually white, which is the color that is most reflective and emissive. These white materials are highly sustainable, adaptable and recyclable, like those that are made by quality companies, such as Duro-Last Roofing. This makes them the ideal choice for people who care deeply about the planet, their city and the bottom line.  

Laura enjoys writing about green living. If you'd like to learn more about Duro Last, please visit http://www.duro-last.com/

By Guest Author - Jessica Lane

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Pressure Drop in the BFW System - Study more, Save More

Objective
The objective of this study was to carry out a pressure drop survey in the BFW system to identify the areas where we can reduce the pressure drop, which will help in reducing the BFW pump discharge pressure so as to conserve MP steam in the turbines.

Existing System
There are two turbine driven pumps & one motor driven BFW pump in ammonia plant out of which motor driven pump remains standby on AUTO mode for an emergency use. Each pump is having a normal capacity of ~200 m3/hr. The steam turbine drives for both the pumps are of condensing types and use MP steam.

These BFW pumps take suction (approx. flow ~295 m3/hr) from ammonia plant de-aerator at ~120°C & ~1.5 kg/cm2g. The discharge of these pumps at ~128.3 kg/cm2g pressure goes to the first set of BFW pre-heaters E-307A/B where it is preheated to a temperature of 165°C by utilizing the waste heat from process gas.

The preheated BFW at the exit of E-307 A/B goes to the next series of heat exchangers E-211A/B for further preheating by the process gas. The provision of a bypass through a temperature control valve TV-84 is made for controlling the final temperature of BFW after both sets of pre-heaters i.e. after E-307 A/B & E-211 A/B. The temperature achieved after E-211 A/B is ~176°C at present load.

The BFW preheated in these two sets of pre-heaters is now divided in two parts. One part of ~130 m3/hr goes to the synthesis loop BFW pre-heater E-502 where, it is preheated to ~273°C temperature by using the waste heat of reactor effluent. After preheating of this BFW, part of it (~65 m3/hr) is used in the adjacent loop boiler E-501 for generating high-pressure steam & balance (~65 m3/hr) is returned back to the front end.

The remaining part of main BFW stream goes to another set of pre-heater E-210 A/B in the process gas circuit, where it is preheated to a temperature of ~ 274°C. The exit of E-210 A/B is then mixed with the return stream from synthesis loop. The combined BFW stream is passed to the front-end boiler drum B-201 through a flow control valve FV-42.

The flow controller FV-42 is also utilized for controlling the level of boiler drum B-201.

Pressure Survey
We collected the plant data for BFW flow, pressures at different locations in the BFW circuit, temperatures. The Isometric data were utilized for evaluating the calculated pressure drop in the system & was compared with the actual one in the plant at existing load.

The results are as below

It is evident from the above data that the pressure drop evaluation was matching with the actual plant condition.

Actions Taken
Based on the above study, it was found that the excessive pressure drop of 8.9 kg/cm2a was there in the flow control valve FV-42 (present valve opening was ~70%) in the front end. So, it was decided to reduce the speed of the BFW pumps in such a way that the valve opening remains at around 85% which is necessary for a better operability & control on the BFW flow & boiler drum level. In this condition the pressure drop across the control valve was ~4.0 kg/cm2a with a pump discharge pressure of 123.5 kg/cm2g against the present value of 128.3 kg/cm2g.

Further reduction in the speed or consequently, in the pump discharge pressure was not justified due to improper control of boiler drum levels on account of any process variation upstream or downstream in the system.

Conclusion

This simple exercise is just to indicate that if you wish you can identify opportunities for energy saving anywhere in the plant. This exercise resulted in a saving of ~0.7 TPH of MP steam used for turbines which was equal to Rs. 40 Lac/Year OR ~100,000$/year.

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