Automated Condensing System
Author - Prateek Verma, Director - Technical, Spray Engineering Devices Limited

Introduction

In the new millennium, the entire sugar industry is focusing on the energy conservation. With the fall in international price of sugar & continuous increase in sugarcane prices, the cost cutting and alternate source of revenue generation has become the necessity of the day for the survival of Indian sugar industry. The condensing system that consumes a significant amount of power is one such area of boiling house where much can be done in running it efficiently with the minimum power. Since, the cogeneration of electricity has become the modern trend of sugar industry, power saved in any area results in increased revenue earning. The author has been able to reduce the power consumption at condensing system by more than 50% in last 4-5 years in several sugar mills. In 1990 average power consumed by the sugar industry on the condensing system was 6 kW-hr / ton of cane, which has been brought down to 3 kW-hr / ton of cane in 1999 and with the introduction of fully automated condensing system the same has been further reduced to 1.84 kW-hr / ton of cane.

The Energy Efficient Fully Automatic Condensing System

The following factors are responsible for the performance of any efficient condensing system:

  • Minimum inlet water temperature.
  • Minimum or no air leakages in the vacuum system.
  • Effective mixing of vapours with cold water to release hot water at almost same temperature.
  • Efficient air ejection through jet nozzles for better & constant vacuum.
  • Optimum pressure at spray & jet nozzles to be maintained throughout the process.
  • The system should operate at low head pumping system at 16-17 meter instead of 22-25 meter head pumps.
Modus Operandi For The Efficient Condensing System

The water requirements of the condensing system depend / vary with the following parameters:

Vapour load

It fluctuates with the massecuite level in pan, steam pressure and plant capacity utilization.

Non-condensable gases

These vary with the leakage levels.

Air-load

It varies with the leakage levels.

Cold-water temperature

It varies periodically with change of day, weeks and months during a crushing season.

On the basis of the above four parameters, the variable quantity of water should be injected into the condenser at the optimum pressure throughout the operation. Any rise in vapour load leads to increase of water in spray nozzle and higher non-condensable gas load leads to increase water at jet nozzle and the vice-versa.

Method of Control of water in the Condensers

Conventional systems

Conventionally the following ‘Pressure Governing Systems’ are used to regulate the flow of water in the condensers:

1. Single valve control

A common valve regulates water quantity by reducing the pressure across the jet & spray nozzles. Control valve does reduce the water quantity in the condenser as & when required but throttling adversely affects spray formation and jet impact due to loss of pressure. As a result of which the efficiency of condenser reduces at lower water consumption, so the basic purpose of reducing the water quantity is defeated.

2. Double valve control

Two separate control valves regulate the water quantity of jet & spray nozzles separately on the basis of varying air / non-condensable gases and vapour load respectively. Similar to the single valve control, throttling the control valve adversely affects the performance, so here also the basic purpose of reducing the water quantity is defeated.

Latest Innovation in Controlling Water in The Condensers
[The automation of condensing system through Nozzle Governing]

To achieve the effective spray formation for condensation and impact for air extraction, spray & jet nozzles should always work at high differential pressure. The water supply is controlled by opening or closing of number of spray & jet nozzles, so a nozzle always works at high efficiency. All the nozzles here are transferring entire pressure energy into the condenser resulting in good efficiency even if the 15% of water is injected into the condensers. In this case there is no loss of energy as in throttling of valve, where almost 75% energy loss takes place after the valve at 50% flow rate (92% energy loss at 25% flow rate). Hence, Nozzle Governing is far superior to reduce the water quantity instead of Throttling of Valve.

The major advantage of Nozzle Governing System for Condenser ensures optimum utilization of hydraulic energy of water provided by the pumps. It also ensures best condenser efficiency even at 25% load.

Comparison vis-à-vis Conventional system for controlling water

Flow Rate (%)

Velocity (m / sec)

Nozzle Pressure (kg / cm²)

Energy Lost (%)

  Conventional Control by Throttling of Valve Control by Nozzle Governing Conventional Control by Throttling of Valve Control by Nozzle Governing Conventional Control by Throttling of Valve Control by Nozzle Governing
100 14.0 14 1.00 1 0 0
75 10.5 14 0.56 1 44 0
50 7.0 14 0.25 1 75 0
35 4.9 14 0.12 1 88 0
20 2.8 14 0.04 1 96 0
10 1.4 14 0.01 1 99 0